RE: Primary Display setting on Dell Precision Workstation T3620 not working
Updating the BIOS to the current version 2.4.2 still doesn't solve the issue.
It seems like the Precision Workstation T3620 - a business grade PC shipped with Linux - may not be a good choice for running a virtualization setup with PCI passthrough (especially GPU passthrough).
The "Primary Display" BIOS settings, although present in the BIOS, are not even intended to work as expected - see post above.
There are other issues with this PC as well: design flaws in the casing and lack of Bluetooth support:
I definitely don't recommend this PC and actually very much regret buying it in the first place.