Two likely possibilities with further detail about each below:
The link you clicked took you to the community on the host instance rather than the copy on your local instance, or
The community is on an instance that’s defederated with your home instance.
When you view and interact with communities and content hosted on another server, you’re technically interacting with a copy of that community/content that’s hosted on your home server and kept in sync with the main copy. So if I want to subscribe to /c/technology hosted on lemmy.world even though my home instance is sh.itjust.works, I need to visit the copy on shitjustworks at sh.itjust.works/c/technology@lemmy.world
If I went to lemmy.world/c/technology, I couldn’t interact because I don’t have an account on the lemmy.world site.
As I said above, communities and content are copied between Lemmy instances and kept in sync across the copies. But sometimes an instance will ‘defederate’ with another, ie cutting the direct connection between them that lets them copy and sync content. In that case, there’s no local copy for me to subscribe to or interact with.
The incorrect link is far more likely to be the issue than defederation, so whenever you run into that issue check the link and make sure it’s the copy on your instance.
Two likely possibilities with further detail about each below:
The link you clicked took you to the community on the host instance rather than the copy on your local instance, or
The community is on an instance that’s defederated with your home instance.
When you view and interact with communities and content hosted on another server, you’re technically interacting with a copy of that community/content that’s hosted on your home server and kept in sync with the main copy. So if I want to subscribe to /c/technology hosted on lemmy.world even though my home instance is sh.itjust.works, I need to visit the copy on shitjustworks at sh.itjust.works/c/technology@lemmy.world
If I went to lemmy.world/c/technology, I couldn’t interact because I don’t have an account on the lemmy.world site.
As I said above, communities and content are copied between Lemmy instances and kept in sync across the copies. But sometimes an instance will ‘defederate’ with another, ie cutting the direct connection between them that lets them copy and sync content. In that case, there’s no local copy for me to subscribe to or interact with.
The incorrect link is far more likely to be the issue than defederation, so whenever you run into that issue check the link and make sure it’s the copy on your instance.