Microsoft authentication completes successfully using the QR code sign-in.
After authentication, the game immediately displays:
"Sign In Required - You may not proceed without being signed in to a profile."
The Xbox profile is never loaded.
Expected behavior
After signing in with Microsoft, the game should load my Xbox profile and synchronize my cloud save, exactly as it does on Windows.
Actual behavior
Authentication succeeds, but profile initialization fails.
What I tested
Same Steam account on Windows → Works perfectly.
Same Xbox account on Windows → Works perfectly.
Cloud save loads correctly on Windows.
On Steam Deck, a second Xbox account (without a Steam license) reaches the expected "Account Mismatch" screen.
Reinstalled the game.
Deleted the Proton prefix.
Verified game files.
Tested Proton Stable, Hotfix and Experimental.
Signed out and back into the Microsoft account several times.
Conclusion
The authentication process appears to work correctly.
The failure occurs after successful Microsoft sign-in, when Forza Horizon 6 attempts to initialize the Xbox profile on SteamOS/Proton.
Since the exact same Steam account and Xbox account work correctly on Windows, this appears to be a SteamOS/Proton-specific issue rather than an account or licensing problem.
If needed, I can provide Proton logs and screenshots.
System Information
Problem
Microsoft authentication completes successfully using the QR code sign-in.
After authentication, the game immediately displays:
The Xbox profile is never loaded.
Expected behavior
After signing in with Microsoft, the game should load my Xbox profile and synchronize my cloud save, exactly as it does on Windows.
Actual behavior
Authentication succeeds, but profile initialization fails.
What I tested
Conclusion
The authentication process appears to work correctly.
The failure occurs after successful Microsoft sign-in, when Forza Horizon 6 attempts to initialize the Xbox profile on SteamOS/Proton.
Since the exact same Steam account and Xbox account work correctly on Windows, this appears to be a SteamOS/Proton-specific issue rather than an account or licensing problem.
If needed, I can provide Proton logs and screenshots.