I just googled stuff and ios user can install this game but arc need to make .ipa file which is the ios version of apk. I don't know about the coding stuff but dev might need to re-write the game with different language code. Just giving some knowledge.
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Even if "re-writing the game with different language code" wasn't a gargantuan task that would take a team of developers at least a year to accomplish (which it is) there's still a number of hurdles for the end user to overcome. The main one being that you can't simply download and install an IPA file like you do with an APK file - there's a whole slew of steps, software and cabling that you need to go through to make it work, and that's every single time an update comes out.
Believe me, I'm not closing off a potential revenue stream just because I'm lazy or contrary. Apple devices are "closed systems". They're specifically designed to make downloading apps outside their store as impossible as they can. If you want to use your phone primarily as a gaming platform - or want to bypass region locks, install adult games or get sneaky access to closed betas - then you need to buy Android.
There's a reason why nobody (to my knowledge) makes iOS ports of Ren'py games ;P