I love the old Mac Pros and even built a trashcan setup for Debian a few years ago. But TBH, they use a lot of electricity for the processing power they provide. If you already have one or can get one for free, great, use it. Linux runs great. But I wouldn’t go to OWC and buy something that would be outperformed by a fanless, low TDP machine these days.
After 26 years of using Linux, I did my first baremetal “immutable” distro install last week.
My youngest son is starting school and instead of the Chromebooks that they recommend, I took a chance and installed Fedora Silverblue on a $200 Lenovo “student-rugged” class laptop. Everything works and he hasn’t had any issues so far. He gets access to the same student platform as the other students through Chrome, but then I can install Minetest and Tux Paint and GCompris as well.
The older kids run Debian stable for years now, but if this works out, I might transition them over next semester.