Hello,
I have LG 38" 38GN950-B, UWQHD (3840 x 1600) with a AMD 6900XT and i can’t run the game at a better resolution than 2048x1536.
Before i got the AMD 6900 XT i used a nVIDIA1080 TI and could run the game at 2560x1440 (on my ex monitor 34" ultra wide) and 2560x1600 on my current monitor.
Also i’m using Windows 11, but i don’t know if it really matters in this case.
I tryed to modify the variables.txt file but it didn’t work, it just defaulted.
I tryed to play Windowed(fullscreen) and it makes the game 2560x1600 BUT the game is under the task bar and i can’t modify the gamma. Plus i can exit the game with the mouse so it’s not fun 
I would like to play the game at 2560x1600 with black bars in fullscreen.
Any ideas?
Update:
I’ve connected my PC to a 27" 2560 x 1440 monitor and i can select between 2048x1536, 2560x1440, 3200x1800 and 3480x2160.
But when i connect my monitor back, 38" 3840x1600, the last resolution i see is 2048x1536…i can’t select any other resolution.
Update2: I’ve connected my monitor to my gf PC, that has my old 1080 TI, and i can see all resolutions until 2560x1600 and i can play with 2560x1600 on 1080 TI / 38GN950-B.
But for some reason 6900XT and 38GN950-B dosen’t work on more than 2048x1536.
AMD 6900 XT - 38GN950-B - max 2048x1536 -???
1080 TI - 38GN950-B - max 2560x1600
AMD 6900 XT - 27" 2560 x 1440 - max 3480x2160 (2560x1440)