I recently bought an old Mac Pro 2013 (trashcan) with 12 cores/24 threads and 128 GB ECC RAM for my upgraded "always-on" machine - total cost $500. Installed Ubuntu 22.04, works out of the box (23.10 had some issues). Unfortunately it's hard/impossible to completely suspend/disable the two internal AMD Radeon GPUs to lower power consumption. I got it down to ~99W consumption when idle, when using "vgaswitcheroo" to suspend one of the GPUs (and it set the other one to D3hot state). My Intel NUC consumes almost nothing when idle (my UPS reports 0 W output while its running, even with 4 NVMe disks attached via a Thunderbolt enclosure). I don't want a 100W heat generator running 24x7, especially when I'm away from home, so will need to stick with the NUC...