Note that the above post-quantum key exchange method was removed in OpenSSH 8.5 (released March 3, 2021) in favor of a newer one:

sntrup761x25519-sha512@openssh.com

So if you add the previous one to your server config, sshd may fail to start after upgrading to 8.5 or newer (8.7 is the most recent release).

I started using sntrup4591761x25519-sha512@tinyssh.org about two years ago, and the new one when OpenSSH 8.5 came out. They've both worked flawlessly for me. Thank you to TinySSH and OpenSSH, and of course cryptographers, for making this possible.