I would actually try to not subscribe to any beehaw communities if you’re not planning to be on beehaw since they’re defederating. I think that means anything you post on those communities can’t be seen by other servers?
You can browse on lemmyverse.net/communities for a list of every single (Lemmy-only) community.
There’s no equivalent browser site on kbin.
However, another way you can search and get pretty much/nearly all results is by using the community search on the large servers of lemmy and kbin. These large servers try to add every single community, so you can search for both kbin/lemmy communities on these
So for kbin, I use https://kbin.social/magazines
and you can search lemmy.world’s communities too. You can do searches on these even without an account