[krzyk]

SMS and authenticator won't work on a dead phone either, so you are left with keeping a paper with backup codes.

[henryfjordan]

Or a second key.

What happens when your first and only Yubikey gets dropped in a puddle? You're also back to paper and backup codes.

[macspoofing]

>so you are left with keeping a paper with backup codes.

It's not magic, there isn't any other way.