Have you got multiple executable files in the game’s folder? If you run Itch’s app from the console, do you get any errors there?
Viewing post in Game won't run from app
Running the app from the console is less helpful than examining the logs from within the app! However, I do have multiple executable files in the folder: there's also a little install script which sets up a .desktop file, and it turns out that itch is running that. Delete it, and "Launch" gives a choice of the right executable or the two Unity shared libraries sitting alongside it.
So, problem diagnosed, but how does the app decide which executable file to run, and is there any way to tell it what the right one is?
Looks like the two Unity-packaged items the Itch app thinks are executables are irrelevant, although as I can't find any documentation on what they are I can't be certain! I can certainly fiddle things so my install script is either not in the way or runs the executable if called by the Itch app. So one way or another it can be fixed. Thank you!