Off the top of my head ...
Since it's all about "apps" these days, where is the impetus to supply an "app" which generates a sequenced QR code every 10 seconds, and which someone could hold up in a video as proof of authenticity, when it's really needed. No code = no verification.
Obviously the seed for the sequence is related to a private encryption key that itself can be verified by whoever needs to.
Not perfect. Bit clunky, But quick, easy and cheap.
Oh, and totally of no interest to all the tech companies *and* political parties I've contacted. Which (for me) is the bigger story.