Fullscreen playback glitch
I've noticed that the last few versions of Premiere CC 2021 have a weird playback glitch when in fullscreen. Random glitch lines appear on the video.
I've tested this in two different systems. The bug occurs on both.

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Chris commented
Confirming George's solution works. Thanks George!
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George Tsirogiannis commented
Solved! Go to Nvidia Control Panel > Manage 3D Settings > Program Settings (select Premiere Pro) > Vertical Sync (turn ON).
This solved it for me.
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Austin Hines commented
I started noticing this as well when using fullscreen playback on a second monitor, even with a timeline that has previews fully rendered.
I'm on Windows 10 21H1, NVIDIA RTX 2080, Studio Driver Version 471.41.
Also tested with a Quadro 4000 with same results.Playback gets progressively corrupted until program crashes. Restarting the program fixes the problem temporarily, but it comes back again.
Screenshots of the errors are attached. The fact that I can take screen shots of this seem to indicate that it's a problem with what is being sent from premiere to the GPU, not with how the GPU is rendering it on the monitor.