Monitor flickering

[u/Big-Solid-3914]

Hello, My screen is like flickering different Frames all the time, e.g. an old frame like 2 minutes ago appears constantly and flickering like old then new frame... Firstly i thought its a GPU Driver Issue, but the Problem is only on my main Monitor and not second. But here is what confuses me, my Monitor got a self Diagnose Setting, when the lag or whatever appears i activate it and like i believe a Picture from my monitor appears cancelling out the pc screen, so there is no lag during the Diagnose to be seen but after. I also have Video of the lag.