HP Omen 24 165Hz monitor stuck in full-screen-color RGBB loop

[Awenir]

Hello all,

the monitor just arrived today.

Setup

I plugged it in following the instructions of the little folded manual  into my main rig intel i7 6700 with an AMD radeon 6600 as primary display port monitor.

The secondary monitor is also an HP 23" but not for gaming, that one is connected  to the 2nd DP input of the radeon graphics card.
(I also have a 3rd monitor which is now re-attached to this system, so- all graphic card ports are fine.)

Problem: the Omen just shows screens of red-green-blue-black, grey, repeat.

ATTENTION ----- Due to this mode there is No OSD available  😞 ----  ATTENTION

Pressing and holding buttons to "unlock" anything is not possible/shows no changes.

The Omen shows the same error when being tested on my laptop HDMI port.

It even does the same color-loop when not being attached to anything.

The thing is, despite only looping the colors both my gaming rig win10 and the laptop win10 detect the Omen just fine(!)

AMD adrenaline would let me choose freesync options for it, too. So... something works inside.

Any ideas are welcome, I am out of testing ideas...  I repeat : with a different monitor the gaming rig works with 2 monitors just fine, switched from DP  to HDMI and back just to be sure nothing fried on my 6600).

I also tried:

all three connector options HDMI 1,2 and DP on the Omen to see if it behaves differently,

tried to keep it without power connector for 30 minutes and turn it on again

tried to "blindly" unlock OSD / Power button (makes no sense, as far as I read the manual this only works when the OSD is displayable)

Is there any shortcut to factory-reset the monitor without the OSD or is this a dead-on-arrival?

Maybe there are some tricks with the control buttons I haven't tried yet to get out of that mode?

I'm pretty much out of ideas for options / tests, any help would be very welcome.

Thanks in advance and kind regards,

Awenir