- Raspbian 64-bit - other than the SEO post title, I will never call it anything but "Raspbian". Alas, poor Ian.
Back up your user files (only). Don't bother configuring the installer beyond choosing "Other Raspbian" and "64-bit base", it ignores your settings, you'll have to configure the device after booting stock. But it writes the micro-SD card correctly; I didn't have to reformat it myself like last time. So I run thru my 400 setup routine again, and with minor changes it's still current.
Everything seems to work. I can run my Scheme scripts in Gauche like it was just a minute ago. Since it's 64-bit now, I should be able to install Chez Scheme from Debian! But ambitious plans later. Python is 3.9.2, which meh, fine; I've mostly updated my desktop to 3.10, but old ports require 3.9 still.
I had a weird crash with Twitch, but I've had that before; on reboot I was able to watch Twitch with no problems, but I'll keep an eye on that.
Uh, when adding things to the Main Menu, make sure they're marked executable (chmod 755 whatever).
And reminder, MagPi magazine is good content, you just have to persistently demand "free PDF", nobody wants dead trees! It does tend towards the very noob, classic WIRED magazine color/font assault on your senses, and they think IDEs are a good idea on a tiny computer. Don't do that. Just use Vim in a terminal.
Very importantly, keep your files as much as possible on a USB drive, not the internal SD card, you don't want to thrash the OS card any more than you have to.
Now the next step will be to reuse my old micro-SD card for an alternate OS, so I'm not running Linux. But if you do run Linux, Raspbian's acceptable since it only has one hardware profile to support.