WetGeek If you open up NVIDIA X Server Settings via Budgie Menu then go to X Screen 0, what are your settings for:
- Sync to VBlank
- Allow Flipping
Additionally if you click X Server Display Configuration then click the "Advanced..." button in the bottom, do you have any of the following checked:
- Force Composition Pipeline
- Force Full Composition Pipeline
Looking at some Mutter changes that landed after 3.36.3 but that was in previous sync so shouldn't be a sudden change there. It may be related to the nvidia-390-glx-driver update. Once we get the settings, we can see if reverting the 390 for your system specifically fixes the issue.