Ah, the remote community federation from actually another instance might be finicky.
Let's take an example: !movies@lemm.ee
- if you click that link, you should get redirected to https://leminal.space/c/movies@lemm.ee , which would allow you to subscribe (that works 100%)
- if you go to https://lemm.ee/c/movies and try to subscribe and then give your home instance, that might not work.
The first option is usually preferred, and that's while you'll see a lot of ! links over here.
A good community to discover communities: !communitypromo@lemmy.ca , especially this post: https://leminal.space/post/15455263