Yep, the same cable. I'm also insecure if it is the monitor. But the checkup via F2 after the start which took hours was fine. Just the long diagnostics on DELL won't work. super annoying, But thx already for the help - much appreciated Update November 3 = a DELL-Cares agent setup a monitor exchange.
Hi everyone, I'm facing the following issue currently: I use two screens, one off them is the AW3420DW. Since 2-3 weeks, the AW3420DW turns on and off all the time saying no connections found when I start Warzone or other high performance programs.  Î tried disconnecting the other display, used several cables (HDMI / DP) and the issue is bigger with HDMI (approx. 10 sec. the screen is off, 1-2 seconds it is on e.g. in Warzone) than it is with DP. There it just flickers once every while. The graphic card (RTX 3090) has been replaced but it hasn't solved the issue. (therefore: all the Dell checks have been done and not issue was found) The other screen (32 inch Dell 4k) works perfectly fine.  My guess it is the display, but then again with other systems it seems to work. Did I forget to mention something? Thanks so much in advance! :)) 
Aurora R11, RTX 3090, AW3420DW