You can subscribe to lemmy communities outside of ttrpg.network.
For example, you found this interesting https://pathfinder.social/c/pf2general
Follow the instruction on the blue block on the right:
You are not logged in. However you can subscribe from another Fediverse account, for example Lemmy or Mastodon. To do this, paste the following into the search field of your instance: [email protected]
example search:
https://ttrpg.network/search/q/!pf2general%40pathfinder.social/type/All/sort/TopAll/listing_type/All/community_id/0/creator_id/0/page/1
now just click [email protected] , and subscribe.
After this, pathfinder will be listed under communities for everyone, and it's easier to join. https://ttrpg.network/communities/listing_type/All/page/1