that's pretty boring.
well at least we can enjoy their content without their limitations, since we see it from a different instance.
use https://federation-checker.vercel.app/ to check is the instance you are considering is blocked by others. and what the instace blocks.
if you see a community for the first time, it will take a while to load the last 20 posts on that community. after that, every time an update is done on the remote community, it will be pushed to yours.
idk if at least one person need to subscribe to it, or just opening it is sufficient.