I'd like to replicate this (a smaller version) but with ECC RAM. It is hard to find mini PCs (or laptops) with ECC RAM support.

Serious question: why would you need one for a home usage? I mean, you can easily reboot it nightly, and nobody will ever notice. Unless your personal server is used by people across the continents, of course. But even then, my SBC reboots within 20 seconds or something. Not really noticeable.

HP and Lenovo have SFF or UCFF workstations with ECC support like the Z2 Mini G9 or P3 Ultra SFF.