If only the two desktop shortcuts are blank, then the most expedient method is to manually assign an icon:

1. Right-click the shortcut for Deus Ex and select "Properties."
   
2. Click the "Web Document" tab if it is not already selected.
   
3. Click "Change Icon."
   
4. In the "Change Icon" box click "Browse."
   
5. Now navigate to "C:\Program Files (x86)\Steam\steamapps\common\Deus Ex\System\" and then select the file "DeusEx.exe."
   
6. Click "Open" and then "OK."
   
7. Click "OK" to close the shortcut Properties.

For Riven (1997), you will need to navigate to "C:\Program Files (x86)\Steam\steamapps\Riven" and then select the file "riven.exe." I don't own the remake of the game that was released last year so I don't know the name/path of the file you should select to assign the icon image. Ideally there should be a ".ico" file with the desired thumbnail image. If not then look for a small ".exe" file with the desired thumbnail.

Stop use windows desktop shortcut icon, yo cant have 100 games anyway, then you hit many more icon , you will learn sooner or later its a outdate windows way to start a game, and steam client has home and collection for sorting.

And you will loose them someday, mark my word if you dont have backup of them.
this is total waste of time in the end how much effect you did to recover it or fix it.

You think a person with 500 or 1000 games use windows desktop shortcut, re-think again.

ps.
I only use use windows shortcut on Scrpts Extended shortcut. rest is move to a dump folder i dont look at ever.

And i wish someone else have told me this long time ago.
Just wait to other steam user dare tell you this, a waste of time with old windows ways.