How can I use ssh -X on macOS Catalina? [Warning: untrusted X11 forwarding setup failed: xauth key data not generated]

How do I get ssh -X working on macOS Catalina (10.15)?

ssh -X linux_host works from another linux machine.

On a fresh install of macOS Catalina, I have installed MacPorts and xorg_server. However, ssh -X linux_host gives the following error message:

Warning: untrusted X11 forwarding setup failed: xauth key data not generated

In attempt to get this working, I changed my ~/.ssh/config file to

Protocol 2
Host *
    ForwardAgent yes
    ForwardX11 yes
    XAuthLocation /opt/local/bin/xauth

however this seems to make no difference.

Please note that ssh -Y works but is less secure than ssh -X.