"Possibly the best alternative to StreetComplete for iOS users at the moment is Go Map!!!: For some time now, the app has also offered a "Quest" mode, which is probably the closest to StreetComplete in terms of appearance and functionality. The Quest brings "some StreetComplete flair for iOS users" The Quest mode in Go Map!! must first be activated via > Display (map icon) > Overlays > Quests (thanks to ThoZick for the tip). In addition to the quest mode, Go Map! can also be used for more advanced editing."
Other alternatives are OSM-Go and MapComplete, which run as a PWA (see also in the linked article)