By and large, you don't go to Discord looking for a community, you find a community by other means and then join their Discord if they have one.

That said, there are ways to look through open Discord servers - those that don't need an explicit invite - and join that way.

A quick websearch turned up at least one site that offers such a service.

Caveats: What they get out of it I'm not sure. I'm not affiliated with any of them and I don't know whether they're connected to Discord the company or not. And if they're not, I don't know if those services screen for bad servers that try to hack your Discord account.

This is probably why finding the community first is the more usual route.