[netsharc]

On Android such a spoof app existed, it can hook into seemingly any API call and return things you control: https://www.youtube.com/watch?v=_dt50HWys1k&t=27s

But of course you need a rooted phone, and rooted phones can't run banking apps, tap-to-pay, Netflix, Pokemon Go, blah blah..

The notification "firewall" is probably not impossible to make. I use Pushbullet, it mirrors notifications to my computer (to the browser extension to be exact), and I can already dismiss notifications coming into my phone from the computer. It should be possible to make an app that intercepts all notifications, analyzes their contents and dismiss them if they're spam...