I use a notebook with a high resolution screen with 200% UI scaling. I have additionally connected 2 FullHD displays with 100% scaling.
Cubase and 3rd party work very well in general. Moving windows between the different screens works flawless.
However, the picker dialogs in Cubase do render with 200% on all screens. So I get very large windows to e.g. select a bus, plugin, send, etc. There is also a big offset of the window compared to point I clicked. Leading to the fact that the window is many time not even visible. On the main screen which uses 100% scaling, no picker boxes are visible at all.
I can use Cubase only with 100% UI scaling set on all the screens.
Do you use a different screen scales and does it work for you?