It sounds like the file type isn't supported for ios (iphone)
the confusing part is that the logo next to the downloads says its available for apple and the only thing I can think of is that its not supported on ios but supported on macOS so you would need a mac device to run it unforunately
the good news is that this game can be run on literally anything no matter how bad of a device it is, its available on most computer-based operating systems like linux, macOS and windows so if you have literally any computer at all you can play it!