There's nothing you can do if you tried the above, it's 100% just the monitor itself. The ROG STRIX monitor you mentioned you had was flagged by several other people for black screen flickers and white line flashes. The main root cause of this is that the panels are notorious for reacting to refresh rate dips and mainly in dark scenes. this is just seems to be a general OLED issue since the tech still has ways to go in terms of improvement.