Sounds like you are dealing with an existential issue. Personally I've dealt with this by learning and teaching others, through this I feel I have found purpose. I also find it through political activism and volunteer work. There is nothing as fulfilling as helping others just because you want to and can.
Lemmy was made by communists, you're gonna find communists lol. As far as I know there isn't anything else particularly comparable. What made you leave reddit?
Saw the archive, I am too young 😔