itch.io

Thanks for getting back to me - I've not got a computer running linux to test it on at the moment, but the following steps were recommended to me as a good starting place: 

1. Right-click the X86_64 file
2. Select Properties
3. Click the "Permissions" tab
4. Check the "Allow executing file as program" checkbox next to "Execute"

Let me know if this helps in any way, if not I'll see if there's anything else