I am keeping an eye out for a cheap M1 Mac Mini on my local Craigslist because once you yank it out of its huge metal case, which is like half PSU, the board itself is quite small. Apparently, the PSU only outputs 12W across the entire power connector, so easily powered by a barrel jack. I quite like the idea of playing around with macOS as a SBC OS, but even just designing a smaller case with sufficient cooling would be fun too.