I can only watch 1080p YT in web player on 1440p monitor in full screen.
1440p videos are little jagged especially with panning. For 4k there must be super best of my ISP day but still not too smooth.
But downloaded videos I have no issue to play 4k h265 in full screen with MPV.
Display in QubesOS not only relay entirely on CPU but also on memory copying.
I could have 48GB RAM in my laptop but in single channel, for dual channel it’s 32GB only (since 16GB is soldered).
ThinkPad T14 gen3 i5-1245U