For me the issue was a dockingstation (I have UtechSmart 1:12 usb-c to outputs) this probably limited the amount of energy the display could get and caused the flickering. My problem still is that I can’t use 3rd monitor without my dockingstation as my laptop doesn’t have enough ports.
I guess my main lesson is make sure you are not overextending any one input. In my case is was the usb 3 thunderbolt port which I tried to connect too much too via the dockingstation