(legitimate, but does NOT support APK→IPA)

is specific to a processor (ARM vs. x86) and an operating system (Linux-based Android vs. Darwin-based iOS). An APK’s Dalvik bytecode is interpreted by ART. iOS does not have ART. Translating Dalvik bytecode to ARM machine code on the fly requires a just-in-time (JIT) compiler – which Apple forbids in third-party apps.

Check if the developer has released an official iOS version on the Apple App Store Progressive Web Apps (PWAs):

to run Android apps on iOS, but this is an emulation, not a conversion, and often requires sideloading. Search for an Existing iOS Version

Most “APK to IPA” websites fall into one of three categories: