question on HP Prodesk BIOS (specifically: Headless Mode)

[ambad4u]

greetings to everyone!,

i would like to know if there is a hidden BIOS option/menu perhaps that can be enabled on HP Prodesk units?
the option would be specifically: "Headless Mode".
tried to find settings in the BIOS itself but no such option.
tried BiosConfigUtility to get/set the said option but also fails.
i've tried it on: 'HP ProDesk 400 G7 sff' & 'HP ProDesk 600 G5 sff'

i had before a Dell Optiplex SFF (unsure if it was 3010 or 7010) paired w/ a XEON
it was able to boot without iGPU or external ones, it beeps the usual "no GPU found" thing but boots none-the-less...

i was under the impression that it would do the same with HP Prodesk/Elitedesk but sadly no.
i have tried it on my: "HP ProDesk 400 G7 sff" with an i5-10400F
it just beeps the usual "no GPU found" and blinks orange or red and loops...

any hints or insights is appreciated!
thank you for reading my post.

best regards,
ambad4u