Oh! That’s actually the reason you DO have a Mods entry btw 
You installed the game on your Windows drive, which seems to be a hardcoded requirement for the gamepass version to display the Mods option.
That’s exactly what other users can fix by making a symlink into the above mentioned folder that points to the actual drive where the game is installed
Here you go, here’s a link to a post explaining the process for those who installed it on a different drive and have no Mods menu