Same here, I put it on two very old RPi 1 and was amazed at how low the footprint is. I wish there were images available for other SBCs as well, mostly Allwinner based ones (OrangePi, NanoPi, etc); probably I did something wrong but building them from scratch turned out more complicated than expected.

Yep, Alpine works well. A GUI can be tricky, though. And none of the RasPi tools (e.g. `raspi-config`) will run because of the different libc.

So, running it on a Pi 5 CM in an IO board, there's no way to tell the Pi what device to boot from.