Directly flashing BIOS from USB never worked for some reason so I ended up installing Windows to update my BIOS. Did it somewhat gradually with a few intermediate updates and successfully updated to 2.29.0.no 8222CL with VRM modd and BIOS 2.29.0. never had 6268CL. to expensive, this is normaly a sign for wide compatiblility, the highcurrent CPUs are cheaper because the limited compat.
Sadly, still same issue, no video output, seems like USB devices turned off, but system stays powered on.
(Also tried CMOS reset and GPU/monitor/cable swap before BIOS updates, same thing.)
At this point I might try to hunt for an HP z6/z8 g4 instead...