I know you are getting frustrated with the situation but maybe a little trouble shooting? You say you have an 12th Gen processor and a RTX 3090 video card.  I will assume you have it on the DP output from the video card.  I will also assume when you installed the RTX that the onboard video was disabled? The 12900k is the newer process that takes quite a bit more power?  If your 3090 card happened to be the Ti version, it also takes more power.  I would think you have a large power supply installed.. But, of course, the basic question would be, have you tried the monitor on another system and does it behave the same way?   When you turn the computer off, does the white light stay on?  I currently have a 3420 and will need to watch how mine behaves during shutdowns and sleep cycles. The suggestion about the UPS is one I would have given also, even though I use one on my system with no problems.  And of course putting it on a different wall circuit might be tried. When you shut your system down, do you leave the power supply on?   Beyond basic stuff, I can only bring up the possibility of the Open Air type system may be missing some circuit completed, like a ground which isn't happening for some reason.  If you are using Win 11, mine even jumps around especially when the background changes.  I will go through the manual tonight and see if anything I can see might help.  Be careful not to plug and unplug it at the monitor. You might even power it down, unplug it and let it sit for the night with no electrical, audio or video connections.
 Forum. DELL-Admin>  Hello,  I have a few issues with this AW3423DW. But right now the most pressing is that a few times a day, the AW3423DW will not power back on after my PC wakes from sleep or is turned back on after shutting down. Power button/stick doesn't do anything. No lights anywhere. The only way I can get it to turn back is by removing the power cord and sticking it back it. And even sometimes takes more than one try. Right before typing this post I had to plug and unplug this thing 10 times. That's TEN times.  I am "upgrading" from an AW3418DW. I had that monitor for years and I never had a single issue with it. I'm going to be packing this lump of stuff back up and sending back to Dell. But I want to know if it's my AW3423DW that's a lemon or if this is a common issue? That way I'll know whether I should get a refund RMA.  Other issues: - Loud fan. It's louder than my open air 12900k/RTX 3090 desktop PC.  - Pixel shift which I know is necessary, is very distracting as the screen seems to jump around a lot more than I could have imagined.  - The AW3423DW was telling me to run a pixel refresh on the first day, 6 hours after it left the box. My understanding is that pixel refresh wears out all the pixels so that they age equally. But it's doing it on the first day, how is this supposed to last longer than a year?  Thanks 
AW3423DW, won't turn on after PC sleep/shutdown