edit: lmao... I dunno why, but Lemmy gave me this post as a recent post, but I just noticed it's a year old 🤦

On the target field

I've not seen the target be blank, but I'm not sure the exact steps you're taking to add the game. Maybe you're copying in an incorrect path? The other thought, you might need to force Proton Experimental in the compatibility tab when you modify the game. If it's a Windows exe for the game, then you must do this, otherwise Steam will not run it. Could be why it is clearing the target?

On the images

Steam is pretty bad about updating the icons and such some times, and since you are adding as a non-steam game you have to manually add all of the images yourself.

Find the game on SteamGridDB: https://www.steamgriddb.com/

My process:

1. Add the game to Steam
2. Run it once and close it
3. Go to it's library page, right-click top banner area
   • Set custom logo
   • Set custom artwork (hero)
4. Click the gear icon and modify
   • Click the grey square next to the game name to choose the icon
5. Click the Home button in top-left of Steam (just under STORE / LIBRARY)
6. It should appear under Recent Games with a horizontal blank image placeholder, right-click to set custom artwork (grid alternate / pill)
7. Go to your collections, find it and right-click on it, set custom artwork (grid)
8. Exit Steam, and re-open

The exit and re-open should refresh the icon you set at step 4.

Potentially easier solution

Use either Lutris or Heroic Launcher to install the game first, this will take care of grabbing all the proper images. Both of these apps have options to "Add game to Steam Library", which will take care of all the above for you.