You haven’t really provided much useable info or details.
Plex normally uses whatever is configured for the primary display in windows.
The quick sync should be as good as the nvidia gpu.
Try disable tone mapping.
Some other questions…
Are you trying to use this headless?
If so, plug in a monitor or hdmi dummy plug.
Is this bare metal or virtualization?
Are you trying to run plex as a windows service? Don’t.
Are you trying to use RDP to access remotely? Don’t.
Without logs reproducing the issue, all anyone can do is guess.
