Not sure how exactly it is on desktop (probably not too different), but on your instance’s mobile site, there should be an option—probably in a hamburger menu or whatnot—labeled “Communities”. Select that and the next screen will have three options: " Subscribed", “Local”, and “All”.

“Subscribed” lists all communities you’re subscribed to (naturally), “Local” shows all the communities that is hosted on your instance, and “All” shows all communities regardless of instance provided they are federated.

Check out /c/newcommunities@lemmy.world

https://lemmyverse.net/communities

This is a good website if you know what you are looking for