With BIOS 7803 now the MB refueses to boot if CSM is disabled, stuck at q-code 3b and CPU red led. To solve a clear CMOS must be performed and CSM must remain enabled.
7501, missing almost all CBS settings in BIOS. EDIT: going back to 6401, so fare there are no good reasons to use newer BIOS versions for 1st or 2nd Ryzen generations.