Game center stuck on loading

Hi!

Have you tried quitting System Settings and then trying again?:

1. Control-click System Settings in the Dock
2. Click "Quit"

You can also try logging out of your Apple ID and logging back in. To sign out:

1. Open System Settings
2. Click [Your Name]
3. Scroll to find "Sign out..."
4. Click "Sign out..."

If that doesn't work, try restarting your Mac: click the Apple () menu > Restart...