All YubiKeys since X have come with PIV slots, multiple slots for different purposes. Slot 9a for example is used for SSH keys, while slot 9e is used for X.
Install YubiKey Manager using your favourite package manager, here we use brew.
brew install ykman
Generate key on YubiKey slot 9a, saving the public key to yubikey-public.pem
ykman piv generate-key --touch-policy always 9a ~/Documents/yubikey-public.pem
To get the public key in a format for OpenSSH you can use the following command to copy it to the macOS clipboard.
echo `ssh-keygen -D /usr/local/lib/opensc-pkcs11.so` | pbcopy
The YubiKey SSH PIV public key should now be on the clipboard, paste the public key to the location that is required. SSH user account, Git authentication, etc.