Average hours spent on mobiles per day per user in 2021
From State of Mobile 2022
Notice that this is just for Android mobiles. It's unclear why AppAnnie didn't include iOS usage in the chart. Possibly it has to do with Apple's App Tracking Transparency (https://techcrunch.com/2021/04/26/apples-app-tracking-transparency-feature-has-arrived-heres-what-you-need-to-know/).
This is one of the many passages and charts Alessandro finds in books and articles on a daily basis. They span many disciplines, including:
Alessandro occasionally adds a personal note to them.
The whole collection is available here.