I'm getting this for every subscription that's not on my home instance, too. It's not just Jerboa though, the same thing happens if I try to subscribe directly on lemmy.world.

Similarly, r/AdvancedRunning and r/RunningShoeGeeks are all that I really miss about Reddit. I'm thinking I'll probably just check in once a week or so on the desktop. They've been great resources for my running and I haven't found any non-Reddit community that's even close.