If you're not seeing the mod tab in the launcher it's actually down to your Xbox accounts Privacy Settings. To fix this please do the following:
- Go to your Account Settings in the Xbox Game Pass App
- Select “Manage Privacy Settings” (this will redirect to a webpage)
- Once you are logged on there’s a selection for “You can see and upload community creations”, select the “Everyone” option. Click submit at the bottom of the page and restart the game.