Question about ASUS GeForce GTX 1080 STRIX A8G GAMING

I would clearly say that the graka is defective. But there is one thing I would try: Try different video cables. If this does not work either, send it back to Digitec or the manufacturer.

so in case of problems, always proceed according to the exclusion procedure. That is, change the driver, change the cable, change the monitor, change the PC (yes, put the card into another computer). If the result is always the same, the card is probably defective. I have often experienced that such problems are due to cheap DisplayPort cables...

Well, not all drivers are always the best. It may be worthwhile to use an older driver. Uninstall the graphics driver once with the help of DDU (Wagnardsoft) in safe mode and then reinstall the current or last functioning driver. Your overclocking may also be set too high, so perhaps reduce it a little (it is summer after all).

Which cable is the monitor connected to ?
hdmi ? displayport ? dvi ? has the cable ever been replaced ? is the effect also present with a different cable ?

Driver Version: 384.76

You write "new monitor" - is it possibly because of that? do you have the possibility to try another monitor?