An error occurred while saving the commentAnonymous commented
This vanished from the context menu on my machine.
As it turns out, OneDrive had stopped syncing.
I have my ethernet connection set as a "metered connection" in order to stop Windows Update from working. I can't have this machine automatically updated and doing that plus disabling the Windows Update service seems to have achieved what I wanted. It no longer updates itself.
As a result OneDrive was "paused". If I right click on the icon in the taskbar and then click the ... icon and resume syncing, the share option returns.