At the current moment, there is no Honeygain application on iOS/iPadOS due to its technical limitations.
Simply put, there is no such thing as a background service functionality on the iOS that would allow the application to continue doing its own thing in the background as it does on the Android-based devices.
As a consequence, without the background services, an application on iOS cannot do anything, unless the application utilizes some kind of VoIP service (Skype, Discord), plays audio (Spotify), or uses GPS to give navigations (Waze, Google Maps).
When an app is closed/minimized, it cannot do anything to rouse itself directly. The only way the app can become active again is if the user does something to make it active, like opening the application again or constantly interacting with it, etc.
We could try making Honeygain application for the iOS, however, it would be inconvenient, as it won't run the background, and will probably cause more frustration for the users rather than actually provide a stable application that allows to share internet connectivity and earn money for that.
As a consequence, it is unlikely that there would ever be an application on iOS devices.