i had to add a none steam game first, right click on the game and fix icon.
this is normal in app.exe or name.ico file or even seen in uninstall.exe of that app.
some have even DL .ico from web because they dont like current.

image and Icon is 2 diffrent things, none steam game and steam image, dont follow same rules. then view in steam

You add one yourself. Steam non games can't add Artwork.
Just right click the blank artwork
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1914605009
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1914612787

The Non Steam games I have in my Steam library include the thumbnail next to it in the library list.

good point Jaunitta maybe this is not even Icon and user that dont know None steam game dont add wallpaper, and Center of Graphic in screen

the library entry not background image. just the game cover image.

引用自 NeBaZ-)：

the library entry not background image. just the game cover image.

there is no game cover image then its a none steam game, thats what im use to see in old steam gui, as Jaunitta explan now you can do it yourself. ( let me explan better i always only kept icon on none steam game so i never forget its added. as nonesteam game. )

okay. I got it. thanks. you really helped.

unwilling to necro but I have the same exact issue after the last update.
Now all non steam games icons are just the default black square.

EDIT: found out now you have to use PNG files because using the exe of a game won't retrieve the icon like it was working before