The Star Wars universe is not a "hard" science fiction setting. Trying to delve into "the science of Star Wars" ultimately leads to a tangle of inconsistencies and contradictions. My choice to use the Star Wars universe rather than a hard sci-fi setting as the framework for my storytelling is purposeful. In a hard sci-fi setting, an explanation must be given for any observed contradictions in the setting or its science. In the Star Wars universe, it is enough to simply handwave issues with some technobabble, or even to just ignore them completely. My opinion on Star Wars TTRPGs is that this response should be encouraged, rather than simply tolerated, in order to cultivate the storytelling mood of a science fantasy space opera.
What follows is a listing of some of the scientific inconsistencies of the Star Wars universe that are either commonly discussed and debated by fans, or else are particularly widespread and foundational to the setting. There are of course many more examples than what's listed here, but my hope is that my treatment of these examples will give a good enough picture of how I think apparent inconsistencies can (and should!) be handled when playing a Star Wars TTRPG.
Across all the various inhabited worlds of the Star Wars galaxy, the vast majority of sentient lifeforms are humanoid. Their societies, in many cases, feel less alien than some human societies found here on Earth. They very often breathe the same air, use the same medicines, and even eat the same foods as other unrelated aliens. The ecosystems of all alien planets tend to share many common characteristics, with most of the planets featured in the Star Wars movies having biomes that look exactly like biomes that exist here on Earth.
The meta explanation for all this can be attributed to a combination of filming technique restraints, lack of imagination on the part of writers, and the desire to craft accessible and human-digestible stories. Possible in-universe explantations might include the idea that all life in the galaxy was in fact seeded from a single source, or that of course there are plenty of more exotic planets and lifeforms out there, but the ones that are shown tend to be Earth-like and humanoid because those are the ones that can be most easily colonized and/or interacted with.
Response — In my opinion, a good space opera storyteller should reject these in-universe explantations and instead simply say that that's just the way life works in Star Wars. If you are setting out to make up your own alien species or planetary ecosystem, try to make something that seems both interesting and reasonably believable-sounding and makes for good storytelling, without worrying too much about whether it's scientifically valid, internally self-consistent, or "alien" enough.
Planets in Star Wars tend to have only a single biome, and when inhabited they tend to be home to a single dominant species with a single unified government, culture, and language. Planets with interactions between two factions are an exception. Planets with more than a handful of distinct populations are unheard-of.
The meta explanation is mostly laziness, and simplicity for storytelling's sake. A possible in-universe explanation might be that inhabited planets and planetary biomes have much more going on internally, but tend to just be simplified down to stereotypes and generalities in the mind of the foreign public and for the purpose of representation in galactic government.
Response — Single-concept planets are a core component of the space opera genre, and the way I see it the trope should be leaned into without needing any justification. If a story or RPG campaign is set entirely on a single planet and/or involves political intrigue, then of course planets should be made as complex as necessary, but otherwise I'd say one-liner planets should be encouraged.
Despite taking place a long time ago in a galaxy far far away, most people in Star Wars are humans, and speak English (*cough* excuse me, "Basic"). Unlike other sci-fi settings (Star Trek, Firefly) which are often set in the future of our own galaxy, thus giving a plausible explanation for why everyone is human and speaking Earth languages, Star Wars has no excuse.
The meta explanation is that the film industry (at least in the 70s) requires humans speaking English. In-universe explanations are typically that Basic isn't actually English, it's just translated in the movies for our viewing pleasure. This could be taken even further and argued that the "humans" in Star Wars aren't actually humans at all and don't look anything like us, they're just played by human actors for our convenience.
Response — This is a fairly meta issue, and so my suggested response is to just ignore it. Don't think about it. Avoid making the sort of comments and comparisons to Earth-humans that make people question why there are humans in Star Wars, or what the relationship is between that galaxy and ours.
Droids in Star Wars are plentiful and widespread. They are intelligent enough and mass-producable enough that all human endeavours, from farming and manufacturing to education, scientific research, warfare, diplomatic protocol, and administration could all be completely automated. Despite this, droids (and automation generally) in Star Wars seem to be drastically underutilized. Most people still have jobs, doing ordinary things that could easily be done by a droid instead. And economics throughout the galaxy is still based on scarcity, with many people living in material poverty, despite ubiquitous high technology and innumerable worlds with surfaces completely covered in automated factories. While these contradictions are also present to a less extreme extent in our modern Earth's capitalism, the economic paradigm in Star Wars has continued unchanged and with no apparent crises or instabilities for tens of thousands of years. Money is a huge part of the Star Wars setting, and yet economics (or even more specific details like labor strikes) is very rarely discussed and never satisfactorily explained.
The meta explanation is that post-scarcity economies are boring. There are possible in-universe explanations that could be debated (reasons why automation isn't always cost effective, or unmentioned labor laws prohibiting a lot of droids perhaps) but I've never seen this issue discussed much.
Response — In my opinion, Star Wars is not a great setting for discussing the economic implications of advanced technology. Stories centering around a labor strike, a trade embargo, etc. should avoid provoking larger questions about how the economy in Star Wars actually works. It just does.
In the 4000 years that passed between the Old Republic setting and the setting of the Star Wars films, nothing really changed in terms of technological sophistication. The ships and droids all come in slightly different shapes, and the latest awe-inspiring superweapon is always something a little different, but technology never seems to have advanced at all. In fact, it could even be argued that technology in the prequel trilogy seems more advanced than in the original trilogy.
The meta-explanation for the apparent stagnation is that the tech level of the movies works well for storytelling, so why mess with it? As far as technology backtracking between 22 and 0 BBY, the issue is that droid armies, clone armies, droid starfighters, double-bladed lightsabers, and R2-D2's jetpack are all things that either weren't thought of or weren't cinematically doable in the 70s and 80s, which is why they only show up in the prequels. A possible in-universe explanation is that science in Star Wars really is stagnant and that despite the presence of scientists and scientific research, nothing new or better ever develops. Another possibility is that technology in later periods actually is suitably more advanced, and it's just that we as the low-tech ignorant audience have no good way of judging that AT-ATs are better than the AT-TEs from 20 years prior, or whether the Ebon Hawk is or is not equivalent to the Millennium Falcon after 4000 years of intervening starship design innovations.
Response — My preferred explanation is that science in the Star Wars universe is studied, and research and development proceeds, and technology thus improves over time. Despite this, technology from 100 ABY is no better than technology from 4000 BBY. There is no resolution for this contradiction. It just is. In game terms, scientific work can potentially improve technology in minor ways, but it should never go beyond the paradigm that exists in the films.
In many ways, the technology in Star Wars is far more advanced than our technology here on Earth: giant spaceships, anti-gravity, hyperdrives, artificial intelligence, holograms, laser weapons. But in many other ways, our Earth technology is at the same level as or even more advanced than what's seen in Star Wars: internet, miniaturization of electronics, wireless data transmission, speed and usability of computers. Surely a society that could make a protocol droid or a star destroyer could make a smartphone, right?
The meta explanation is that it's hard to predict the course of future technological development. It's possible that in-universe explanations could be crafted to explain why Luke Skywalker's datapad is less sophisticated than the phone I'm currently typing this on, but I haven't seen any.
Response — A hallmark of the space opera genre, at least for me, is that it's got that 70s feel. The fact that Star Wars is a product of it's time period and feels unavoidably like someone from 50 years ago tried to imagine the future is, to me, a feature not a bug. An analogy could be made with how the steampunk genre is based around Victorian writers' predictions for the future. The technology of Star Wars should not be updated or fudged to match what we now see as the path for current and future technological progress. It should be kept pure in it's 70s aesthetic, with all the inherent contradictions that entails. [Note that this applies only to technology and the genre's aesthetic. There is no reason why racism, sexism, cisheteronormativity, or any other problematic feature of Earth's past and/or present should be carried forward into modern sci-fi storytelling.]
Spaceships in Star Wars always seem to move more like airplanes, rather than how we now know spaceships to maneuver. In real life, space travel is all about acceleration, relative velocity, trajectories, orbits, and escaping gravity wells, whereas in Star Wars it seems like it's all about absolute velocity and flying directly from point to point as if there's no gravity in space at all.
The meta explanation is that airplanes are more intuitive to most people than spaceships. Attempts at in-universe explanations by describing movie scenes in terms of physics and orbital mechanics are generally painful, pathetic, and hopeless.
Response — Physics in Star Wars just works differently. That's all there really is to it. Generally, the physics of spaceflight (and all other science in Star Wars, for that matter) should be assumed to work the way our intuition supposes it would. To go somewhere, you need to point yourself in that direction and push. The more you push, the faster you go. If you stop pushing, you slow down. Things in space don't generally come to a complete stop ever, but without a working engine they just sort of drift around slowly regardless of how fast they were moving at first. Ships can orbit planets/moons/stars, but if they are flying around near planets/moons/stars without orbiting them, then the planets/moons/stars don't influence spaceflight much at all. Notice that I am not saying things like "space has friction" or "planets only exhibit gravitational attraction under certain conditions". I'm not suggesting Star Wars has its own separate but internally consistent physics, I'm saying that the good thing about Star Wars is there's no need to worry about logic or consistency, just intuitive reasonableness and good storytelling. [Similarly, the are no relativistic time effects in Star Wars. Time obeys our intuition of moving at the same pace for everyone everywhere.]
This is one of the big ones everyone always likes to point out. There's no sound in space, so why does Star Wars always have sound effects when things explode?
The meta explanation is that good sci-fi action movies need lots of explosion noises. The in-universe explanation I typically see people toss around is that the ships in Star Wars must all be fitted with some sort of sensor-linked system that simulates the explosion sounds for the benefit of the crew.
Response — This one's simple and obvious. In Star Wars, there actually is sound in space. Deal with it.
Lasers can't combine with each other like they do when the Death Star superlaser fires, and laser beams can't self-attenuate or deflect each other the way lightsabers do.
Response — In Star Wars they can.
Asteroid fields are actually very spread out, they aren't dense enough to be a hazard to ships flying through them.
Response — In Star Wars they are.
Nebulas are way too dispersed to interfere with visibility or communications or anything like that.
Response — Not in Star Wars.
Creatures like mynocks and giant space worms can't actually live in the vacuum of space.
Response — In Star Wars they can.
And is there really just one set of industry standards? A single power cord or data stick can plug into every computer in the galaxy?
Response — Yep.
To summarize, if you are playing a Star Wars TTRPG and find yourself asking sciency "how" or "why" questions, I am asking you to Quit With All That Nerd Shit. Science in the Star Wars universe just works. It works inconsistently, often self-contradictorily, and intuitively. It works the way the 70s science fantasy space opera genre aesthetic makes it seem like it would. If you're looking for a hard sci-fi role-playing environment, look somewhere else.