How to create an custom share screen when receiving a share in a flutter app(or on Android and iOS native) like the pocket app?

Question

I want to show the screen of a custom app like a demo, not the default share sheet, when I click Share in an external app

I already checked the below issue and didn't understand it in that android answer How to make an overlay when sharing into app in android?

It will be implemented in a flutter app, and answers on how to implement Android and iOS native are also welcome

demo

[demo gif] [demo gif]

demo png demo png

I tried using WindowManager to share sheet using Intent.ACTION_SEND in Android, but the important thing is that pocket app doesn't ask for systemAlertWindow permission What APIs are used to draw over other apps (like Facebook's Chat Heads)?

I want a custom screen to appear when sharing my app from outside, rather than simply floating my app on top of other apps.