Why don't devs use React Native like tech stack that allows development across platforms at the same time, especially for simple apps like this when they probably don't have to use all native capabilities different platforms provide.
Yeah you basically need to write your own screen time api for android and use the draw over permission - it's going to be an interesting build for sure!
Technically, the icon displays the app as paused from the time limit. Once you surpass the time limit using the app, you can stop using it or allow you temporarily (1 minute to 15 minutes or stop limiting the usage for today) to continue to use it.
It's a neat option to have this on your phone, but I usually keep expanding my time limit more than just quitting the app.
I think that's what this app is aiming for, allowing you to use the app more time requires more effort than 2 taps.
Also it would be better if you kept Instagram uninstalled... I see it installing on the screenshot!