NTRU in OpenSSH
OpenSSH has supported post-quantum cryptography for several years now.
email@example.com (hybrid Streamlined NTRU Prime and X25519) was introduced in OpenSSH 8.5. It was made the default key exchange mechanism in OpenSSH 9.0.
The reason it is a hybrid mechanism is that the security of NTRU is not as well-established as that of X25519 and other classical methods.
Note that this for key exchange, not authentication. But considering that post-quantum cryptanalysis is a future concern rather than one situated in the present, that is what is worth focusing on right now. After all, someone who can break your key exchange in the future can record your encrypted exchanges now and decode them later. But they cannot travel back into the past to impersonate you in the present.