Ai app for ios and android

I have an idea of an ai app that adds a button to your phone screen on every app and when clicked it will read and scan your screen then sends notification with written information so you can see the result instant on the same screen you want to scan for ai answer, i have a little bit of knowlage about ai and how it works and have the experience on ux/ui designing, from your guys experiece. Where should i start from? Should i start with the app design or the ai part? Which platform is the best for building ai phone apps? I would appreciate any type of advice!