I have added a foreign (non steam) game to steam library. If I right click at the game in the list and choose properties, a new window appears. There you can set to force use specific proton version, set game name (instead of seeing an exe file name as game name), also if you click on the square near it, you can choose an icon that will be used for the game when listed in library.
But I do not see an option there how to set a game banner image (the big picture that you see on the top when you choose the game in libray). Currently there is just blackish rectangle and the text of the game name.
Is it possible to add a background image for the non-steam game?