German authorities warn that state-controlled cyber spies are targeting high-profile individuals on Signal and WhatsApp.

Germany's domestic intelligence agency is warning of suspected state-sponsored threat actors targeting high-ranking individuals in phishing attacks via messaging apps like Signal.

I honestly do not see what other method should be used. QR codes are pretty good to transfer information locally. I mean sure, you could ask the user to type it, but I do not think that is practical ...