Many thanks for taking so much time to assist me with this, but I'm a lost cause.
I have already mentioned that "tinkering under the hood" is not for me - I couldn't care less how Linux works (or doesn't - see 22.04).
Linux would best be served by an exclusively GUI system in which the terminal is hidden by a devilishly difficult search process. All I want to do is find the section called "Backup/Restore", click on "Backup", tick the box for the Hitachi and click on "Continue". All problems would then be solved by the erasing, initializing, partitioning parts of the backup software. I am not interested in file systems, etc - my sole interest is in two mouse clicks and then watching it all happen without a hiccup.
It's sad that such a superb OS has become a playground for bored, whatever, coders. The same applies to all the distros. It also says why so few users switch to Linux - "never have so many hindrances been put in the way of so many potential users" to paraphrase somebody.
I have backed up my HDD to Google Drive and that worked straight off. If only it were the same for my Hitachi external drive. People should look at MacOS Time Machine to see how it can work.
Many thanks again.
Martin F Slater, CH-Luzern