Stupid question: I thought that PeerTube is also ActivityPub and that therefore it should be possible for me to subscribe to a PeerTube channel from my Mastodon account.

But I just tried with this channel (not an endorsement, I haven't seen the videos yet, I was just curious about interop between Mastodon and PeerTube), tried copying its ID and pasting it into the Mastodon search field on here, and it just gives 404...

Is it simply because we're not federating with them, or is it some sort of software issue because of them running PeerTube?