Hello @Pöna
I have no idea what causes that issue. I have read lots of arguments on the NVIDIA forum about it. Seems to come down to a driver issue apparently. All I can offer is a couple of suggestions...
1. The most suggested fix is to remove the graphics drivers and clean install an older one. Which one for your 2060, you will have to experiment. I imagine it will have to be a very early one compatible with the RTX series.
Use this tool to uninstall the current driver with. It helps to remove all of the remnants of it.
https://www.guru3d.com/files-details/display-driver-uninstaller-download.html
2. Turn off G-Sync.
3. Try Display Port if you're using HDMI.
Fingers crossed.