For me, I have MSFS on a non-system drive, so the location is:
G:\WpSystem\S-1-(Windows User ID)\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
BE SURE TO MAKE A BACKUP COPY - it can reside in the same place under a different name, like My 20211011 Old Usercfg.txt
You can edit the file with a text editor like Notepad.
After you make any edits, make your new usercfg.opt file read-only to prevent MSFS from changing any edits back. Such as if you change any LODfactors for terrain and object in the usercfg.opt file, MSFS based on the Graphics settings options (make LODfactors for terrain and object are 200 right now in sim) won’t change the values back.
I think it’s been announced for SU6, IIRC, that MS is going to allow LODfactors for terrain and object as high as 400 so one won’t have to edit usercfg.opt. Don’t know about the VR factors, though. I changed mine from 1.0 to 2.0 in the .OPT file and thought it made a difference with an RTX 3090.