I’ve read that it should be possible, but my experience seems to show that that is incorrect, that you need a login for every instance where you wish to make a post or comment. Could someone who knows clarify this?
If you need a login for every instance of Lemmy to participate in non-local communities, then that will, I think, be the #1 issue with Lemmy adoption, and the main reason folks bounce off.
You have to find the same community in your home instance, instead of going to that instance directly.
I agree this is confusing, especially if you come there from a link. There’s no easy “go to this community on my instance” link right now, though there are user scripts to make this easier.
What you can do is copy a link to a community or post and paste it in the search on your home instance. That’ll hopefully show that post and allow you to subscribe.