Hi I have the same problem with 32:9 (5.120 x 1.440) ksp2 supports it and it works just fine if you set it in C:\Users\USERNAME\AppData\LocalLow\Intercept Games\Kerbal Space Program 2\Global\Settings.json
It would be very nice if this can be selected without editing the file.
WIN 11
Ryzen 7 3700X
32 GB DDR4 RAM
AMD RX 7900 XT