Debian is always pleasant
Upgraded my main home Linux fileserver/do-everything box from Stretch (9) -> Buster (10) -> Bullseye (11). Usually I just install the new OS and hand-copy my config files back into place, but I decided to try the OS upgrade.
Impressed that it all worked flawlessly. Only two hiccups:
(1) Had to uninstall my ancient 9.6 version of Pg and install the new one (a few apt commands), which the installer didn't do automatically for reasons I didn't bother to read because it was easy
(2) Buster setup a suspend schedule which I had to diagnose and remove. That was the only major foul.