The QR scanner in the camera stopped working suddenly, after I used it a few times

Ede-ita ~ See if it works after doing this:

Restart your iPhone

õ¿õ¬

You might also try launching your camera in QR-Scanner mode using Control Center as described here:

https://support.apple.com/en-au/guide/iphone/iphe8bda8762/ios

Also, not all 2-D codes are “QR Codes” … attempting to scan a non-QR code will not create any response by the camera.