It was a bit of a shock when I upgraded my Debian systems to Bullseye (11) from Buster (10) a year or so ago. I discovered that the wiki I've been using for years, Moin Moin, was removed because it didn't support Python 3. I've a lot in the wiki and was in no position to migrate, so I made a wiki only VM and keep it at "oldstable". Since none of it is internet-facing, I can keep it this was forever, even once all support ends. I'd rather not have to have another VM though.