Try uninstalling or -at least- Disable NVIDIA GeForce Experience and see if that puts an end to this problem.  I'd also disable Dell Update, Dell SupportAssist, (Dell) Fusion in Start>Run>services.msc too. Double-click each "Dell" entry and change its Startup type to Disabled. Don't change anything else. Just close the services.msc window when done and reboot.
Since buying my XPS 8950 in April 2022 I have gone through an issue fixing process with DELL support (e-mails in my non-English native language). There is no online track record of this correspondence, so I think it is helpful to start my question with a summary of the process thus far: April 2022 onward - Initially had two problems: (1) When starting up the machine. Pressing the power button caused the machine to make some start-up noises but the two monitors were not recognized and remained black. The 'solution' I found was to power off the machine with the power button and then to power it on again shortly after. This problem did especially occur after a night of being turned off. (2) The monitors sometimes turned off (black) and on again a minute later. This happened both while working and when leaving a short break with screen saver mode turned off. May 2022 I replaced my Displayport cables with brand new ones, and I temporarily disconnected the 5 year old DELL monitor and only worked with the new DELL monitor I bought in March 2022. Neither of these measures addressed the problems. June 2022 - Not related to the problem, but probably good to mention. I expanded the default 32GB DELL memory with two extra Crucial memory cards (2-16GB DDR5-4800 UDIMM 1.1V CL40) to reach 64GB in total. I have had above problems both before and after installing the memory. August 2022 - I reached out to DELL who replaced my graphics card the next day. This solved the power-up button problem, but not the random black screens problem (problem 2 above), so a few weeks later (August 2022) DELL also replaced my motherboard. Unfortunately the black screen problem came back again a few weeks later. 3 October 2022 - I had been installing DELL and Windows updates all these months. However, I never looked at the NVIDIA icon at the right bottom corner in Windows. I discovered that if you right click on it you can enter the NVIDIA GeForce Experience, which indicated that NVIDIA drivers were never updated since I bought the machine. It seemed that I had to first create a NVIDIA account and only after creating an account the NVIDIA driver updates could be installed. After that all my problems disappeared, no more random black screens :-). Somehow the Dell driver status check never identified this.  7 October - After installing Dell driver update 0.1.6.0 the black screen problem came back. So, I repeated the NVIDIA GeForce Experience driver update process by clicking reinstall drivers and that fixed the problem again. 14 October - While working on the machine I briefly noticed a terminal screen with the words "Dell Trust" in it, so I suppose some update or modification was made by Dell to the system. It went quick, so not sure what exactly it was. Directly after this,  the black screen problem appeared again and it kept annoying me the rest of the day. Next, I repeated the manual NVIDIA GeForce Experience driver update (reinstall) and that fixed the problem again. To me it seems that Dell driver updates and NVIDIA driver updates are somehow overruling each other in a problematic way (not sure if that makes sense, I am not a computer expert). It is nice that I have this manual NVIDIA hack to temporarily fix the problem. However, it would be good to know whether there is a more permanent solution. For example, can I tell Dell to never alter NVIDIA driver installations? The Dell support e-mail address has not responded to any of my e-mails since September 28 (3 weeks ago), so not sure  whether they lost interest or simply cannot offer a solution. This is why I am now reaching out to the community.
XPS 8950, black screen and possible driver issue