I too have noticed this. But since you mention the phone model and number of cameras… are you saying it worked on another device?
My assumption is that they lean on Google Play Services for QR code scanning.
So without it, it will not work. But i have also noticed that it does not help to install microG, so i can only assume the implementation there is incomplete.
See API implementation status here.
Hint: it is called “vision”. Supposedly it should be complete for “barcode”, but which sounds like it means QR codes too.
My hypothesis for why BankID works is that they ship their own QR library, but i did not verify that.
I’ll do some more digging in the log and see if it sheds any light on things.
What does this have to do with Swish, the Swedish payment app?
Its QR codes are not swish:// urls, so it is not obvious that out-of-app QR code reading would help in any way.