Enable root login on the server, but restrict them to passkey only. Set up a key pair on your local box, put the public key in root's authorized_keys file on the server and off you go.
This is 99.9999% as secure as not allowing root logins, as long as you protect the keypair from theft.
If you set up a complex pass phrase on the key, then you'll need to be present to run the backups, or use ssh-agent or something similar. Or, you could just not put a pass phrase on the key and you now have magic, passwordless access to your server via root. Obviously, in that instance theft of the private key is a more serious issue, so you need to understand those risks and either mitigate them, or use a strong pass phrase.
I know this isn't quite what you asked for, but honestly, passkey protected root logins are safe (with the caveat that you should keep up-to-date on sshd patches).
Any other option that allows any user ID enough permissions on the target server to be root, without putting them behind a passkey protected ssh login is actually less secure, than just allowing root via passkey only.
If your local workstation has a predictable IP address you can make this even more secure using the