Android has the greatest mobile OS market share by a massive margin.

It’s my understanding this is true globally, but not for the US, where Apple has ~60% share.

(This app should absolutely be cross-platform though)

There’s probably significant overlap with the Linux warriors here who will respond to people’s legitimate questions with variations of “why don’t you just not do that and instead do this other thing that doesn’t solve your issue” (and also not explain how to do that either).