I have used the Stellaris launcher to add a mod to the Steam workshop for the game of the same name, but after doing so, it appears with a blank thumbnail:
Going from the steam side of things, you can manually upload an image, but there doesn't seem to be an option to select it as the thumbnail:
I can't for the life of me seem to find anywhere to actually set the thumbnail. The in-game upload screen seems to be lacking this as well.
Is this something doable in-game, or is there some workshop setting that I'm missing? (There definitely are mods for this game with thumbnails)
Best Answer
I'm sure by now you solved this, but I'll leave here my answer for others that may encounter this issue. I had this issue too with my mods https://steamcommunity.com/id/savalina/myworkshopfiles/ and didn't find any help elsewhere, but I sorted it out.
Make sure you add the thumbnail tag
picture="picname.png"in theyourmod.modfile, not in thedescriptor.modfile located in your mod folder.