Ubiquiti is really taking up the slack in some areas Apple has abandoned.
I bought a UNAS-2 (and a couple of 12 TB IronWolf Pro drives) a few months ago when the "time capsule will not be supported in a future version of macOS" warning first appeared. It has been outstanding alongside the rest of my UniFi setup, and perfectly supports Time Machine backups. The UniFi Identity macOS app means my family's computers always stay authenticated/connected and my wife & kids don't have to do anything to make Time Machine just work.
If you're a power user who loves the Apple aesthetic and you already have a UniFi setup at home, you'll feel right at home switching from Time Capsule to a UNAS.
What format is the destination drive? My ideal is APFS clone backups to a remote drive, but I don't know if there are any network setups that support that, even though you can do it to a local drive.
I was under the impression that's how SMB TimeMachine backups work currently
Have you tried it also working to backup files from Linux and windows machines ? Was hoping for a good mixed backup solution and I'm getting Ubiquiti would deliver here.
Also why the 12TB ironwolf drives specifically ? Personally I always was a fan of buying true enterprise (the ones designed for "online" or near line storage) but sometimes specific models and sizes of random drives do very well in Backblaze testing
I don't have any Linux/Windows machines, but I've seen nothing that would dissuade me from using it when I eventually migrate my current laptop to Asahi Linux.
As for IronWolf Pro drives, I chose them because they seem to have similar longevity to enterprise drives with less noise (my equipment is in a closet under the stairs).