Snort, primal and iris don't support Communities.

I'd probably say snort and iris are borderline defunct (imo). Nostrudel.ninja is the best out there for web.

You can find communities you've joined on amethyst by going to the signal type thing on the lower bar, and then going to the communities tab. Or going to the All Follows at the top of Home feed. Unfortunately this isn't not obvious and there are limited functions there. (You can't create communities, or approve posts.)