The M1 Mac Mini could work! The actual PCB for it is tiny compared to the size of the case it's presently in.

Project video for a shrunken mac mini by Snazzy Labs- https://m.youtube.com/watch?v=pQWGFKhBQwU

As others pointed that you could scrap a m1 mac mini (I own one), also is really another powerful processor and yet power efficient than the m1 readly available and with linux support? I find hard to believe, also it seems that mX family will be popular enough to have out of the box linux support, IIRC all the asahi work will be upstreamed, while I bought a raspberry and the linux support is awful, considering all the years raspberry was already available, most distros does not support it and you rely on a lot of hacks to make them run (I do prefer arch linux over all other distros), also the raspberry is not suitable for my use case, I wanted a workstation with low power consumption and there is none besides m1, maybe in the last 2 years a new one came out that I’m not aware of.

I think the idea being that both the M1 and the RPi are ARM64