This may be the solution to launching your game, When i first bought the game it wouldn't launch.
Googled but couldn't find a solution...

This may fix it for you:

1. If you don't have the Ubisoft launcher(Ubisoft connect) download it here:
Ubisoft Connect[ubisoftconnect.com], and try to launch it and then hit play in steam.

2. If you already have Ubisoft connect, fully close Ubisoft connect (background also) and launch it again, then go to steam and click play.

This worked for me so hopefully also for you!