Not present with a Pixel with Android 16, my effective choices are:

1. App can't use mobile data in background

2. App can use mobile data in background except in Data Saver mode

3. App can use mobile data in background regardless of Data Saver mode

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For anyone doing comparisons, the literal settings appear under "Mobile Data Usage" as:

* [X] Background Data ("Enable usage of mobile data in the background")

* [ ] Unrestricted mobile data usage ("Allow unrestricted mobile data access when Data Saver is on")