A massive effort has been underway for a while to get an iOS build of the app: https://github.com/streetcomplete/StreetComplete/issues/5421

Open source software often moves comparatively slowly, of course, but I believe they're making decent progress.

No, but: https://github.com/streetcomplete/StreetComplete/issues/5421

You can use a different, webbased one: https://mapcomplete.org