Some additional thoughts on why alt accounts don't seem to work here even though people have no issues participating in multiple separate forums. Last time I said it was because I can interact with the same people and posts regardless of which account I use.
The problem is, as usual, the microblogging paradigm. Sure, I could create multiple accounts and only follow furries on the furry account, software devs on the software dev account, etc. But it would never work because microblogging is unfocused. You can post about anything and there are no repercussions in going offtopic. You might lose some followers, but that's really it. Many people wouldn't care.
Even if we all started off on the basis to keep topics separate, it would fall apart very quickly. As soon as others stop doing it, it stops working for you as well because then all the software devs you'd been following would suddenly start talking about politics, sports, etc. Fediverse instances having a theme doesn't solve this because federation mixes them all together anyway.
In contrast, forums were focused on a theme and there was a staff to make sure it stayed on track. Alt accounts may serve other purposes, but they can't be a substitute for taking part in separate communities.
Volpeon