If instead of googling for 15 seconds you had any real experience about developing apps that need to run in the background (like I do), you would know that this 'background running' is a joke.

The only way to run an app non-stop is to have a persistent notification. And even then, apps are killed off left and right by the likes of Samsung. See https://dontkillmyapp.com for more details

It depends on the phone. Lots of problems with eg the COVID-19 exposure notification apps where firmware updates from Android OEMs were needed to whitelist the apps, the user accessible background settings weren't enough to keep them working.

Nope. It's Google apps. Users aren't asked for a choice there.

And then maybe "what app a user selects", if the user manages to follow the procedure.