It took me far too long to recognize that the toubles I was having were simply related to driver versions.
I was upgrading/swapping quite a few PCs in the family, because top hardware new hardware enters for professional use and then cascades towards kids and extended family and friends for many years who get to game a lot more than I do.
The current upgrade cycle was really more about making Windows 11 work on officially unsupported hardware, but quite a few GPUs got swapped along the way.
While I was working in my home-lab, which includes two 42" 4k screens in cascaded KVMs, one really annoying symptom was that the primary monitor, which typically runs at 10Bit full RGB and 144Hz, on a VR panel would refuse both refresh and bit depth and revert to a non-RGB TV mode with reduced bits for color, giving rather ugly color edges to TrueType font hinting especially with HDR. Oddly enough the secondary display which is a strict non-HDR IPS panel capable of no more than 60Hz at 8 or 10 bit pixel depth, runs just fine at those optimal settings.
For a while I was thinking this was just a limitation of older hardware (a GTX 980ti was involved, as were various GTX 10* series cards), but then even RTX 40* series cards were showing those same symptoms... but only on Windows 11 24H2, not on Windows 10 22H2.
So I was ready to make M$ the bad boy (always a popular option), but when I was also playing with Intel and AMD GPUs, swapping back to an Nvidia card typically activated an older Windows driver from around Summer 2024... And that one didn't have those issues with display capabilities! Turns out I was running Windows 10 still on the December 2024 CUDA release drivers, while I was upgrading to the latest "Game Ready" drivers on Windows 11!
After some more elaborate testing I've come to believe that the display capabilities detection code for the new drivers is the main source of my problems.
If it's a laptop GPU (e.g. an RTX 4060), no issues using current or last-gen drivers, with internal or external display, but I'm not using a KVM there and it's strictly 1080p.
If I use HDMI straight from the GPU, again no issue with 10* to 50* series GPUs even on the critical 42" display at 10Bit fulll RGB and 144Hz and HDR: pixel compression is likely at work, but it works as expected and as it has done for years.
But the dual 4x4k KVM is DP, and on a 10* to 40* GPU, with 2025 drivers, that primary display will only do 60Hz at 8bit YCb*422 (or 24HZ at full RGB), probably the last resolution to do 4k without pixel compression, yet with the RTX 5070 it will be fine
Reverting to a 2024 driver on either OS eliminates the issues for 10* to 40* GPUs.
So my current error theory is that negotiating for the vastly expanded range of display connector speeds and capabilities is broken for the older generation hardware in the new drivers. Where 50* series GPUs could drive these high resolutions without pixel compression, neither my screens/KVM, nor the 10*-40* series GPUs can support those speeds and require compression, but fail to negotiate properly with 2025 drivers, falling back onto the highest resolutions possible without compression.
2024 drivers are much more likely to negotiate for compression as a default at 4k, because even the GPUs couldn't do without, even if displays could.
Just with my setup, the amount of GPU/screen negotiation going on, every time I switch between systems is truly mind boggling: ATEN, my KVM providers has explained to me that they cannot really retain state during switching but need to treat it like a full set of plug/unplug events of two DP monitors and the sheer number of potential resolutions, refresh rates, color formats and bus speeds has been very large even before the new speeds, resolutions and formats now supported with Blackwell and RDNA 4 came along.
Still, if you're in the GPU business, that's simply what you have to deal with and sort out.... soon, I hope.
BTW: I didn't really observe any game related crashes, but I typically just bench games a bit: it's the family that gets to play, I tend to work on computers.