If we're talking playing chess at what is currently represented by a FIDE 2800 rating, then yes, it is literally impossible for some people. That shouldn't be controversial at all.
As for the "it's definitely possible otherwise we wouldn't have a world champion" I don't know what to tell you other than that "logic" makes no sense.
Once again, context. That thread of discussion was regarding a mother asking a coach if her child could be world champion. Judging the potential of a child is a fool's errand. If you look at Magnus' first few FIDE rated games in the database, you might wonder if he would ever reach 1800. If you take a look at games just 2 years later, and it is like they are not even the same person playing. So, saying "no, your child cannot possibly reach WC level" is asinine. You can get away with it because you will only be wrong 1 time in ~300M, but it is still inaccurate to say it that way (though, again, I don't disagree entirely with a coach telling a parent that as such a question tends to come from parents who push their kids too much and managing the expectations will lead to the kid enjoying it more - doesn't change the fact that "impossible" and "improbable" are not the same thing).
But calculating a probability (1 in 300M) is just an approximation we use when we don't have all the information. In reality a single person is either 100% or zero percent. Either they have that potential or they don't. In practice it's useful to believe in yourself, I'll agree with that.
And if it's just a random person, then you're right, you can't say for sure they wont or can't be world champ.
But if it's a coach and student, then yeah, it starts to make sense to say the kid is not good.
Would I think Carlsen as a 9-10 year old is garbage? Maybe, but maybe not. I met a talented kid once. He was probably rated about 1000, but the things he saw were clearly different from any other beginner I'd played. I got excited and started asking his brothers about him (much to their annoyance).
Yes, and Finegold became a GM at 40.
He even wrote a book about it.
But guess when he made IM
Self fulfilling prophecy? Sure. Could I be 2200? Sure (I really think so). But 2800? No. Can anyone do anything? No, and frankly it's childish to believe otherwise.
I wouldn't use Finegold as an example there as he was basically the world's strongest IM for about 20 years. As I mentioned in the earlier post, Ye Jiangchuan is a better example (starting at 17, competing for a shot at the world championship at almost age 40).
And I wasn't saying "Hey, Mr 2000 ... you can be 2800 if you really want it!" I was saying, if you wanted it and worked at it correctly (by identifying and addressing your weaknesses - assuming the weaknesses are things that are fixable. If you have narcolepsy and fall asleep during games and lose on time, there is only so much you can do there), you could reach 2200, or 2300, and possibly even 2500 (assuming you had enough time to work on your weaknesses and play in enough tournaments to do so). Is it likely? Well, that is really up to you. It is definitely possible. I would say start with the goal of reaching 2200 and then reevaluate. You tell kids to "reach for the stars" so they don't set their goals too low. For adults, they should be wise enough to set reasonable goals and incrementally update them; but that doesn't mean the stars are not possible! It simply means you get there by focusing on your next step and not on the horizon.
IMO hard work will (usually) let people go far beyond what they think their limits are.
Is it possible for me to be 2500 if I had an ideal scenario? I think the answer is no, and I don't mean that in a negative way, I just mean in a realistic way.
Chess is definitely a performance game. A 5 hour game seems like a lot at first, but it's not. It's very limited. To play at a high level it's all about preparation but also performance. Think of it like boxing. I'm in my mid 30s and out of shape. Could I hold an international boxing title? No. It's just not possible anymore because I can't preform at that level.
Oh, your profile says you're in your mid 30s. I guess neither of us wins that pissing contest as we're the same age.