1. Field of view (FOV)
Add custom values to configuration file
%USERPROFILE%\Documents\My Games\Starfield\
Create a new file called StarfieldCustom.ini, if it doesn’t exist.
Under [Camera], add or modify the following parameters, where X is the desired value:
fFPWorldFOV=X
fTPWorldFOV=X
2. Pillarboxing
Modify the game executable to remove pillarboxing
Open <path-to-game>\Starfield.exe in a hex editor (e.g. HxD).
Search for as hex
8E E3 18 40
Replace it with
AB AA AA 3F (for 4:3 aspect ratio)
or
00 00 A0 3F (for 5:4 aspect ratio)
Save the changes.
(https://www.pcgamingwiki.com/wiki/Starfield)