Can you try checking for updates through Steam? Maybe the install isn't complete. Try qutiting and restarting Steam, and if it still doesn't help, check to see if there is a log.txt file in the X-Plane Steam folder (it may have more info):
- Start STEAM. Goto LIBRARY.
- Right click on your X-Plane 11
- Choose Properties.
- In the rising window choose LOCAL FILES.
- And than choose BROWSE LOCAL FILES.
- Now you are in the X-Plane 11 Main (Root) Folder and you see the path in your file explorer.