This has been done already, so no. There’s prior art. Look up Clef for one example.

https://en.m.wikipedia.org/wiki/Clef_(app)

I had high hopes for Clef, but unfortunately, it never got the traction it needed.

That would require each site to implement server-side components to talk to Clef, and most sites have been ice age slow to implement basic TOTP never mind yet another method.

Now, if the big existing OAuth sites, your Google, Facebook, Okta, etc implemented a QR code method like Clef then it might work.

I already need to do this to login to LINE on my computer, so no

do it. no one's going to sue for you implementing a random comment brainstorm.