Would ADHD even exist in a closed, perfect environment where a person’s intellectual and emotional needs are met?

Meaning some science fiction post-scarcity world where you can get everything you need by magic? ADHD would exist, but it is likely fair to say that it could easily go unnoticed. ADHD most stands out by its impact to interaction with other people. If you have no reason to interact with other people, then you can likely avoid the impact. It is possible for ADHD to even impact one's own personal interaction with themselves, but without interaction with other people, you're not apt to know what you are doing is any different.

But ending capitalism by transferring capital away from private interests to community interests is not that. All it would see is moving the capital to community interests. That capital still needs the exact same human involvement to maintain function. You are still going to go to work like you always did. You are still going to have to remember to pay your bills like you always have. There is no magic in that – just a slightly modified legal system.

Does ADHD exist in small, non-developed villages and communities?

A non-developed village won't know what ADHD is to diagnose it, but the qualities will be present in some people. I mean, ADHD is thought to be genetic, so if that community doesn't have the right gene line it might not exist, but I don't think that's what you mean.