tl;dr - At first, while the USB boot and installer worked, ROCK never loaded due to an issue with the integrated network card. Using a Cisco/Linksys USB network adapter, everything is working fine on my Mac Mini.
I wanted to use a very old Mac Mini as my “NUC” rather than buy a NUC PC.
It’s a very old Intel Core Duo dual-core Intel i5 and so old, it can’t even run Mac OS beyond “Lion” 10.3. It doesn’t even have a SSD as suggested.
My needs are simple. I use Tidal and about 8 endpoints that include Sonos and a couple of Ropieee devices feeding DACs. I don’t do any upsampling or DSP functions. I don’t manage my own library of local files either.
Surprisingly, this MOCK with spinning disk is working great. Turned out to be a great low cost solution for now.
[Moderator Edit: CPU specification corrected]