It seems every monitor is affected by this black line going across the top of the monitor, the ACER Predator X34 has the same issue, it happens when you overclock the panel
Could you do this test for me.
Go to Personalistion then background, select solid colour and then select the gray on the top right line, the last one of the top line
You might notice there is a black bar going across the top of the monitor. I have found out this is due to the 100hz overclock and when you turn overclocking off the black bar is gone. I wonder if this is something that will happen with all monitors after a certain amount of time