This only works if the developer uses app indexing where Google can search through the content and make it searchable to end users and other endpoints. It doesn't come for free so Google has no access to things like your bank app's screen.
On the other hand, it's not clear to me that the user opts into the indexing, so Google might suddenly silently be getting access to a huge number of user's deep within-app data without them realising it. But that is old news, app indexing has been around for a while.
App indexing makes sense when you have more stable content inside of an app like a traditional public website. Think Yelp and their 'screen' per place inside of the app. It doesn't make sense to publish the contents of a chat conversation to Google's app index -- that would be a huge privacy leak! It would be the equivalent of GoogleBot indexing my Gmail inbox.