I have never been able to launch FM from the xbox app on PC. I have done the following to try and resolve this:
Updated all windows updates.
Updated all graphics drivers
Updated microsoft store and xbox app.
Reset store and xbox app
Run repair on store and xbox app
Run repair files on Forza Motorsport (FM)
Uninstalled and re-installed FM (multiple times at various stages)
Scanned system files with SFC
Ran a hard drive scan
Turned off firewalls/allowed FM through the windows firewall
Tried running game in compatibility mode
Tried running game as administrator
Done a clean boot and tried running the game.
Deleted all XBL credentials from the credential manager