I don't get it even after reading the guide. How do you deal with backups when using YubiKeys? The private key is stored on the YubiKey with no ability to export it, ok... then what do you do when you lose the YubiKey?

Are you supposed to have multiple YubiKeys (multiple private keys) and then ensure that all your systems accept the matching multiple pubkeys?

The guide's Backup section is... super vague. It says exporting keys, of which some are private keys, which I thought shouldn't be possible?? And then it goes off about partitioning and filesystems?