That game has a comment section. You might get answers there.
Both your questions seem rather independant of the game, but specific to your operating system and "sideloading" software. Itch is not an official apple store.
Also, since when does an iphone count as a mac? Did something change, can users now install software on their iphones, like they can on their macs - if they find the buttons to press to install software not coming from an apple store? Now that would make thos iphones more usefull indeed.