The video in this link show what's happening.
The driver is the latest 19.1.1 jan 20.
Since this is a new PC, I don't know if past drivers have this issue.
Using freesync? Try turning that off if so.
I had that problem with an older driver, with newer drivers I can't use freesync at all (screen goes black). I guess the same thing will happen for some when using freesync and watching ytube video's which run at 60hz.
I do have some screen flickering when watching 60hz youtube video's which was fixed with older drivers and it's back now again.
Would be nice if there was an option disabling freesync automatically for watching video's.
Try driver 18.11.2 btw.
I try to install the driver 18.11.2 but I am getting this message.
It seems that the driver version is not compatible with the vega 8.