I participated quite a bit in r/whatsthisbug and r/spiders helping identify bugs (mostly spiders) for people. It was something I really liked doing, especially educating people about how spiders aren't things to worry about. Guess I'll just head back to iNaturalist for that content.
Other than that, more niche gaming communities were a big one for me. r/puzzleanddragons is a mobile game I play often and the sub was super helpful for news and game discussion/guides. I hope it can kick off here.