If you have one of these beasts linux installation can be a pain.
Seems they use a 32 bit efi for the boot. So when you put any of the standard CD disks - yes disks as booting from USB doesn’t work - it hangs asking you if you want method 1 or 2….
Early disks of ubuntu or fedora will boot but then you have to do a series of online updates. A total pain.
I did want to do a Arch install but debian works - as ever so thats what I did.
Debian will boot if you you use the mac image see; http://cdimage.debian.org/cdimage/daily-builds/daily/arch-latest/amd64/iso-cd/
Described in the following blog;
I did eventually get Manjaro linux installed by using a 686 net install version.
It boots well on the 2.1 mini boot and but you must ensure when installing that you set the whole thing up to boot in BIOS mode on all the install options. No 32bit UEFI.
Finally the MacMini is working again as it should not dragging its OS arround.