I'm just setting up a firebase database for my kivy app and the first thing I need to do is "add an app to get started", the choices being IOS, Android, Web or Unity. Is this saying that I need to set up and maintain code for an Android-Kivy app and an IOS-Kivy app? The idea behind Kivy is that it is write once, use everywhere so I'm hoping to just have one version.
Or have I misunderstood this part?
If you want to target both Android and iOS for any cross-platform development tool (not just Kivy), you will need to add both an Android and iOS app to your Firebase project.  Firebase doesn't know anything about Kivy (or Flutter, or Unity), so you have to tell it which OS is being targeted.
Firestore authentication asking to select "android/ios" or "web" for kivy app