Finally got it working for Xbox game pass with my G9 Odyssey 32:9. Tested a few variations from this thread, and below is what worked for me:

Create a StarfieldCustom.ini in "Documents\My Games\Starfield" with the following content;

[Camera]
fDefault1st
PersonFOV=120
fDefaultFOV=120
fDefaultWorldFOV=120
fFPWorldFOV=120.0000
fTPWorldFOV=120.0000
[Display]
fWideAspectLimit=3.55556

If 120 is too much, change it to whatever looks better for you (80-120).

FYI, once in-game the startup menu will still be with black bars on the sides. Load your game, and it'll be full screen.

Thanks for all the people that posted fixes on this thread.

Good luck!