I've looked into this before but all the QR scanners I've found use some random chinese software which I definitely don't want to install. Do you know if QR code scanners really need this software or are they natively supported in windows 10? Any recommendations?
You're right, even open source libraries are mostly chinese, go figure.
Are you comfortable with the command line? You could try this webapp (requires nodejs) that in theory lets you scan while being offline: https://github.com/gokulkrishh/qrcodescan.in
I prefer copy-pasting the invoice text. Feels safer and I need no additional tools.