Critical thinking courses would indeed be very great to have.

Mere factual knowledge transfer is not effective in forming mature and responsible minds if critical thinking is not a focus of education as well.

I've had people tell me things were impossible because they "Aren't in our list of known unknowns" or they violate some principle for vague reasons they don't understand... then a month later an article shows up saying "We proved that thing Sera said was totally possible"

Scientism is such cringe

Sadly I find people who most proudly preach the wonders of Critical Thinking, are the ones least capable of it.

I think you missed the point, I believe in the Scientific Method as one of the best ways to measure that which is objectively true. It can make no statements on the subjective however, nor the metaphysical.

However the problem is, too many people act as though we've reached the limits of what is possible to know with the sciences and treat it to be "Science's Infalliable Word", when the very nature of Science means we'll gladly throw out anything we already "know" to be true if we find conflicting evidence, and the world has been better off for it.

Heck the definition of "Dead" has changed several times because we keep learning that it's more like a spectrum than an on and off switch, which has so many implications that it makes my head hurt.

True, but I feel like this should be saved for the dumbest of the dumb. Too much cringe has been created by things like Rational Wiki inadvertently getting otherwise intelligent people to believe that doing science is just the ability to shout the name of a fallacy you feel your opponent has committed, whilst oversimplifying anything you don't understand until it sounds stupid..... Ya know like Evangelical Fundementalists do to defend their biblical literalism?

It has culminated into a behavior I like to call the Fallacy Fallacy

It leads to shit like this

Normal Person: The doctor says I have cancer, but it's still treatable, so I should take this medicine, it's expensive, but it'll be worth it.

Scientism Worshipper: I dunno, you think you have cancer because the doctor told you? Sounds like an appeal to authority. Normal Person: Look, my aunt ignored her diagnosis and she was terminal within weeks and dead within days after that. I'm not taking any chance

Scientism Worshipper: Hrmm... So the only thing that has you trusting this doctor is anecdotal evidence?

Normal Person: You're right! These meds are too expensive anyway -Weeks Later-

Scientism Later: Well my friend is dead

Third Party: Because you killed him, he died because he didn't take his medicine...

Scientism Worshipper: CORRELATION IS NOT CAUSATION YOU BIBLE-THUMPER! GO BACK TO WORSHIPPING YOUR SKY-DADDY SHEEPLE!

That's a Strawman in and of itself, but you get my point

Now it may sound like "Well, I guess we shouldn't question the science then."

No, always question the science, that's how you do science. The problem comes when you think you've mastered the science so well (despite evidence to the contrary) that you refuse to let what you know to be questioned.

What is "dumb"? What is "intelligence"?

I think, as long as people have normally functioning brains, it is possible for them to understand. And I think nurturing critical thinking is an important aspect of how to approach this.

You can absolutely present a complicated topic to someone who isn't educated in that field, or even has low education at all, if you are being humble about how you explain it and try to meet them at eye-level.

You don't need to give definitive answers, you may give recommendations, but you can always explain a bit and note that there is also a lot more to it than what you explained and that one must take care before making some further conclusions.
Interested people in your audience then have some first basis and grasp of a topic and can take it up on themselves to dive deeper; for example, by asking questions or finding further sources (you might refer them to these).