I’ve already started seeing a lot of redundant communities being made here that have already existed on other Lemmy instances, and lemmy.ml is at risk of centralization and overload, so now is a great time to raise awareness of other instances.
For science topics, mander.xyz has a lot of good ones set up, and [email protected] on slrpnk.net has been great!
edit: for new users - you can type ! to begin autofilling a community, even for ones on other instances, like I did for the solarpunk community above. It may take a few seconds for the autofill results to show up if you have a slow connection like me.
Only if your server already knows about the community. If you’re the first person on your server (more likely if your server or the one you are subscribing to are small) then you’ll need either the full URL or at least the [email protected] part.