I think a lot of what people experience as free will is just rationalization after the fact based on past experiences and internal belief/value systems.

Yeah I'd agree with that except that it's not a rationalization, it's more like acceptance of reality and the only sensible way to think.

You could add that a mind with free will is a massively complex information processing system that can't be predicted from the outside. It might be deterministic and repeatable, but even if you had access to a copy of the mind, you couldn't input the exact same real world inputs to predict an outcome. At least not outside of a laboratory and artificially created world. So it's not about "couldn’t ever make a different choice" but that the choice cannot be predicted from either outside or inside.

Maybe something like the second law of thermodynamics: "Free will of a mind is the tendency to be unpredictable without full knowledge of all external and internal information".

So you theoretically could take free will away for a known simulated mind in a controlled known simulated environment. Otherwise even a simulated human mind running deterministically on a PC would have free will.

Looking at neurological pathologies or cultural differences is interesting, e.g. leasure time, or more time to grow up as a teenager and access to education has a huge impact. As does the increasing disinformation on news and social media. The concept of free will is useful to improve our society to allow people to make more conscious decisions. Or to understand how people are more and more programmed to say and think certain things because the "technology of propaganda" is advancing. Simply having access to truthful information and having time to think increases our potential for consciousness and free will. In our nihilistic and postmodernist times this is important.

Of course, most of our decisions are made subconsciously without thinking. But a simulated human mind on a PC could go back and examine why it has made a decision. Maybe temporarily rewind and see what decision it would have made in a slightly different mood or with more information. It could then learn and train itself to be more conscious or even edit itself. So being actually deterministic would not decrease consciousness or free will, it could increase it from the perspective of a mind.

So whatever you think about the mental phenomenon, it is a useful and valuable concept from the perspective of the mind(s). Obviously the universe doesn't care but that is it's problem 🌌😜