Hey guys. I found the solution. I only had to force the game to start windowed.
In steam rightclick on supreme commander FA --> Properties and write in Startoption :
/windowed 1920 1080
...for HD Resolution. in my case it was:
/windowed 5120 1440

hmmm. I think there´s no solution. I don´t know. I think I give up. Thx for answering so quickly...

Maybe its important that I have the Samsung G9 monitor (32:9)

Yes I tried to launch it in steam first

Win 11
I9 10980 XE
64BG RAM
RTX 3090

Hi. Everytime I tried to start a game, I got the following error message:

Any "how to" for me pls?
(My graphic drivers are always updated)