I think I got my first smartphone when I was 23, I never use them for anything other than calling, youtube, and basic web browsing
My typing speed on a phone is something like 15 wpm, on a computer keyboard it's 110 wpm
The idea of using a smartphone for anything pleasurable (other than youtube) is totally foreign to me
There was a QR code reader that worked for a long time, then one day it autoupdated to give you popup ads. The only way you'd know it was this app that caused them was if you knew that was the only recently installed/updated app.
There was a second way. The play store let you sort apps by "recently used". This app would prominently be the most recently used app because it did the popup ad as a background task. The "see recently used apps", one of the best ways for non-technical users to have agency over there own device, was removed shortly after.
Both Android and iPhone just allow you to use the camera app now. You just tap on the QR code and it shows the content/link and you can tap on the link to go to it.
It's the reason why the last couple of years it has taken off.