I did the upgrade procedure to move from 11 to 12. Most things went just fine, but for some reason hplip was uninstalled and I could not print. Manually installing the correct hplip package allowed me to reconfig my printer and that was working again. The other thing that broke is my sound. The sound server changed from Pulse Audio to Pipe Wire. The sound worked with Pipe Wire but it was putting my sound card to sleep. On my motherboard, it must engage some kind of high impedance state because it causes a loud 60HZ hum. The solution was to turn off the feature that sleeps the sound card. It's a desktop system, not a laptop, so I don't care about saving battery. The config was actually in the /etc/wireplumber/main.lua.d set of configs. Besides all that, Debian 12 is great, as it has been since I started using it in 1997.