[AdamGibbins]

Does it only support ecdsa? Surprised they don't use ed25519 in their example.

Edit: nope, seems ed25519 supported too https://manpages.ubuntu.com/manpages/focal/en/man1/ssh-keyge... although internet seems to suggest hardware support is far more limited. Tried generating one on MacOS and indeed my Yubikey seems unsupported.

[jlgaddis]

Unfortunately, you can't use Ed25519 keys unless you have the latest/newest model(s) of Yubikey and that Yubikey came with at least a specific firmware version (5.2.3, IIRC).