Yes, I'm aware of the general comments, I was trying to get to the core/specifics. For example, you mentioned multiple times that hardware breaks, can be stolen

Yes, I'm aware of the general comments, I was trying to get to the core/specifics. For example, you mentioned multiple times that hardware breaks, can be stolen, the interfaces aren't standard. But all these things are actually true also for your phone: it breaks, it can be stolen (probably much easier than your keys), and chrome extension+push notification I wouldn't really call it more standard than USB. Again, I'm not trying to downplay Krypton, I like the phone solution a lot, I think it's much more usable than security keys. I use push notifications all the times e.g. via DUO. But I still think we need physical security keys against online attacks, for example as a mechanism to secure your phone itself.