Thank you, Andrew and Charles. I seem to have two sets of macro modules in VBA:
(I have uninstalled NoteStripper from my PC but it is still showing up.)
The macros menu doesn't show up every single macro. New ones that are in VBA sometimes don't show up but when I try to create it as a new macro I am asked if I want to replace the existing one, and I can 'step into' it easily (so far today). It simply doesn't show up.
The macros menu I get when customizing keyboard shortcuts is not exactly the same one as for customizing the quick access toolbar (in the same document).
I unlinked OneDrive on my computer but it was up and running again today, so I've set it to stop syncing.
I suspect that I'm looking at two different sets of macros here, most of which overlap as they derive from the same source. It's been suggested to me that I delete one of them and see how that goes. That still doesn't explain why a macros in VBA doesn't show up in the macro menu, however.