The article uses RSA 2048 :-(. See https://blog.g3rt.nl/upgrade-your-ssh-keys.html for why Ed25519 should be preferred, even over RSA 4096 (assuming it's supported, of course).
Yubikey currently supports 4096 bit RSA keys as a part of GPG applet. There's a PIV module, however in terms of elliptic curves it only has ec256 and ec384 and I still can't get ssh and pkcs11 to pick up anything other than built-in 2048 RSA keys.