> Listing the apps installed on my phone should give me the option to sort them by “Latest installed”. I am pretty sure that if I had had this option and I had seen a QR Code Scanner installed just a few days ago, it would have immediately grabbed my attention. As it is, the way Android lists the installed apps is pretty useless for this purpose.

I was able to find it pretty quickly by going to:

Settings > Battery > Usage Details > Battery Usage Since Full Charge

This showed me the most recent app used. As I hadn't used the QR scanner app in quite some time, it seemed a reasonable place to look first.