In case of interest, it seems I somehow downloaded an update of Darktable a few months or so back unintentionally as a snap package. That would make sense as I noticed (I think from 4.2) that a much reduced database of cameras/lenses was showing up in lens correction. I found an old post on here:
in which it becomes clear that snap packages can’t access the lensfun database on the system and so I followed a link posted by @paperdigits to a flatpak update of Darktable.
That’s now installed, though I had to import several months of images back to the library. I’m guessing my image database might now be a bit all over the place and I will have to reconfigure the new copy of Darktable again.
Thanks again for the help
PS. And now all your instructions on installing initialworkflow work fine. Sigh