My Pixel 7 uses qr.code.scanner.qr.code.reader version 1.0.13 from Aurora St.
If I try to identify with Itsme on an official site (ex My Minfin Belgium) using my Ubuntu PC, I have to try 10 times before succeeding. I use Firefox, Brave or Chrome : same issue
If I do the same test on a DELL Windows 10, no problem, it works right away
Do you have an idea ?
You understand that a problem with the display of the QR code on a certain screen may occur.
Try it with Binary Eye from F-Droid? (My Favorite QR-Code Scanner).
Have you tried scanning it with the built-in Camera app, rather than a third-party app?
I think that is the way to go. All my banking is with an external TAN generator (chipTAN), but for one bank I have to login by using their photo TAN app. The app uses the camera and works on my Motorola G32 with iodé ever since I own the device; very reliably and I can tremble like an 90 year old 
I think the problem stems from the PC running Linux. The Itsme helpdesk gave me some pointers, including checking how Brave, Firefox and Chrome were installed.