If you’re looking at subscribed or All they do, but the local feed is the default, and that only shows stuff on the local instance, in this case lemmy.world.
If you mean your profile, that will show all your activity on every instance.
Yeah, I’ve decided to at least give it a good shot, to try and see if I can stick with lemmy and mastodon. My current problem is I’m finding it really hard to find people to follow on mastodon, and to find enough active communities on lemmy to sate my social media appetite.
I’d say separate. You can only interact with the other instances through your instance, and while they use the same protocol, lemmy and mastodon are just fundamentally different styles of communication that don’t mesh well together.