Oh man, awesome long shot (thank you)!
It was indeed RTSS (RivaTunerStatisticsServer), which I have been using at launch in recent months for some G-Sync game optimizations!
I’m still able to let RTSS run and do its thing and I no longer get UE5 d3d errors if I add a profile for the main UnrealEditor.exe as an Application Profile and set its detection level to: None
