Check out ttrpg.network

dnd@lemmy.world is one, and it has a lot of others linked in the sidebar.

It’s DnD focused but you can still get general advice that’s system agnostic.

All the others I can think of right now are on ttrpg.network, which someone else has already mentioned.

I heard the foundry tabletop discord has some nice people.

You can kinda just open up tabletop simulator and there will be a bunch of people