I've found AM4/AM5 boards will still boot Linux without a discrete or integrated GPU, running a GPUless CPU, not an APU.

It was sorta required by IBM PC compatibles, but is not required by UEFI which supports serial console (or other interfaces).

IBM PC assumed existence of graphic output and sometimes Option ROMs did really too crazy things with it, I still have shivers when I hear "intel raid card" because of that one with possibly Win3.x in ROM...