So it might be, that the itch app does not know the executeable? Based on the wording, I assume OP trys to run the game with the itch app on linux.
If the game was not built on a linux, will the executeable flag be set correctly? It's been a while. But you had to have the flag and have it set for the user are logged in or the group, or no running of the game would commence.
If the game was built correctly, one could simply do a
ls -la
to see the files that have the x flag.