Something tells me this isn’t the last word on the issue. If the fediverse concept is to succeed, then its two (current) largest players need to have some cross-functionality.
I strongly disagree here. They might be using the same protocol, but the user expectations are something completely different. I've tried mastodon and really don't get the appeal, just like I never understood why people want something like Twitter. And I'm sure there are some Mastodon users out there who can't be bothered about Lemmy.
Forcing them into one common framework feels like alienating both to me.
A simple network sniffer is enough to figure out what sites the app is connecting to, then you can just block them on the router.
If you are using Android, you can do that easily right on your phone with PCAPdroid, it's on the play store. No root required.