If you have an iPhone and a mac you can just use the native Universal Clipboard <3
Otherwise yeah, something tied to your account like a google drive note or protonmail draft. The caveat here is that technically the information will then pass through those systems, which could break privacy depending on your trust in <google/protonmail/etc>
A more secure way would be to use photons for the data transfer. Get a QR Code scanner app on your desktop and scan the QR Code displayed on your phone.
I wonder if morse code or some similar audio standard could be used to transmit addresses or invoices
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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?
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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.