APU board? They are going EOL soon, but these devices are built like a tank. Full Linux x86_64 support, coreboot bios. https://www.pcengines.ch/apu.htm A few sellers in the EU still have them.

I use a mixture of systemd-nspawn and different user logins. This is sufficient for experimentation, for actual use I try to package (makepkg) those tools to have them organized by my package manager.

Also LVM thinpools with snapshots are a great tool. You can mount a dedicated LV to each single user home to keep everything separated.

After many years of using multiple devices and even servers with Archlinux installed it never broke because of an update (spoiler: I use systemd-boot instead of grub). If a system is to be used by a less experienced user, just install linux-lts Kernel instead.

Unstable does not mean it crashes/breaks often, it just means it does not guarantee to not bump to the newest upstream version and that it does not do backports. This can be a problem when using unmaintaned software that does not like using a recent python/php.

This is also great because if you find a bug in a software you can report it to upstream directly. Debian maintainers only backport severe bugs, not every one of them. It can take over a year for new features to arrive - especially painful with applications like gimp, krita, blender, etc. You can use debian-unstable of course, which is close to upstream as well.