[snyft]

I had the same problem - it is the problem of the Windows compilation itself and the screen refresh / poor resource management error. It can be solved in this way - increase the priority of the process - from normal to "above normal" (never real time). The downside is that you have to do this every time you run kodi. ( my problem https://forum.kodi.tv/showthread.php?tid=355684 )

I have the same problem as OP, this solution does not solve it. My setup is simple.

2080ti. HDMI direct to TV. Sony 4K (set to 1080p, 60Hz) as I use it for desktop stuff. Makes no difference if you set it to native 4k.
The monitor is DVI. ASUS Ultrawide (3440x1440 120Hz) (gsync on/off doesn't matter)
Audio is via a wireless headset (not to disturb others)
Windows 10 May 2004 Update (fresh install)
Changing settings in Kodi/fresh install doesn't change anything.
Kodi 4.0.3
Nvidia 451.77 (been through 2 or 3 drivers)

I don't really use the PC while I have Kodi running, so hasn't been a big issue for me.

I think you use DP on your monitor? DVI can't handle 4k60 or 4k120 if I remember.
I also have Sony TV though XG950 to be precise hm. Maybe it's the 2004 update.