I'm building a mobile game and only want to use Firebase for Android push notifications (side note: if there's a better way than Google Firebase Cloud Messaging, let me know). I don't want to use it for iOS because I can't build from PC and you don't need it for basic push notifications on iOS anyway.
The problem is, when I load the Firebase SDK into Unity, I keep getting an error "Firebase iOS builds are not supported on Windows. Please build on a OSX machine instead."
It doesn't stop me from building the game, but it's very annoying and I'd like to not have any errors.
Is there a way to suppress this error, or some configuration I need to change?
Reading through the source, it looks like you should only see that issue if you're on Windows and your build target is iOS:
EditorUserBuildSettings.activeBuildTarget == BuildTarget.iOS && Application.platform == RuntimePlatform.WindowsEditor
You should be able to avoid the error completely if you select Android as your build target before opening in Unity Hub:

You can also change to Android in your build settings window:

This setting should be sticky, so you should only have to do it once (unless you switch back to iOS).
If this is not possible, you can also try setting your platform to "PC, Mac, & Linux Standalone" -- although this might not be workable if your project (or related plugins) are setup in such a way that you can't reliably test in Editor like this.
For next steps if the above doesn't work: