Appwrite cross platform (mobile)

Hi, I’m new to coding apps. I’ve been watching YouTube videos ext on setting up a backend server for storing data from my app. I have used appwrite and the iOS platform when creating a project.
I’m using react native to produce the app, by adding the android platform to the project, does this make my project cross platform or will I encounter problems. I’ve read into flutter and the react native sdk beta. However I would like to use something more reliable while it’s in beta.
I want to be doing a test of the app through App Store and google play before September and I can’t find anything online that i understand enough atm to choose.

(The app would be a todo list giving real time input updates )

Thanks for your help, Max