unable to find the file could be due to bad installation. You could try to re-install.
unable to find the file looks as the begenning of the standard itch launcher error. This the error message is much longer. Could you paste it here?
Also you could try to run the game via the command line. Error message could be more help full this way.
- Open a terminal
- go to your ich directory (1)
cd celeste./Celeste
note 1: if you don’t know where is your itch directory, there is “(cog icon) Preferences” menu at bottom left of the itch interface. Then under “Install Locations” heading, there is a [Manage install locations] button. Click on it to see where your games are installed.