I just published a new iOS version of a login-only app. You can find it on the App Store by searching for “Thunkable”. Please install it and register to see its basic functionality.
The app is a template and is open source (blocks). To build an app in which users register, login, and edit a profile, begin with the template then add your own screens and behaviors. This tutorial describes how to build your own app from the template code.
Please send feedback on the app. Internally, it uses Firebase for user authorization, a Google sheet for storing profile data, and Cloudinary to store the profile pics.