We already have the Mac Mini, but an A14-based SBC would be less of a stretch than an M1. A picoMac, so to speak? That would almost inevitably run MacOS by default rather than Linux, though.
The GPU is make or break for Linux. No GPU means it's just another server in a different form factor.
The GPU is make or break for Linux. No GPU means it's just another server in a different form factor.