Guide to run AC Brotherhood on the steam deck (and bypass Uplay requirement)

Bypass Uplay requirement on Steam Deck

Step by step

• First - you need to link your Ubisoft with your Steam account (Do this even if you played any Ubisoft game via Steam before!)
  
• Download Steam version of AC Brotherhood
  
• Using Desktop mode on deck, download latest version of Ubisoft Connect and place it into /home/deck/.steam/steam/steamapps/common/Assassins Creed Brotherhood/support/GameLauncher/ folder
  
• Delete old UbisoftGameLauncherInstaller.exe
  
• Rename UbisoftConnectInstaller.exe to UbisoftGameLauncherInstaller.exe
  
• Start the game, log in Ubisoft Connect first time.
  
• Exit to Gaming mode and start your game, it should work

So far - this method works with most of legacy Ubisoft games I've tried.

Source: u/NoOn3knows