Thunderbird & Provider for Google Calendar sync problem

I am having to work on a backup machine on which I have installed T’bird Profile Manager so that I can import a zipped profile from my workstation while original has a problem.
I have been able to use the imported profile without any difficulty and my add-ons mostly OK but I am having difficulty syncing the Calendar.
Provider of Google Calendar is installed, enabled and available from the Events and Tasks menu but when I open the Calendar I can see all the calendars installed, all but 2 being shown with a button labelled ENABLE. This includes “Shared on Google.”
OK I click on these and they appear as enabled but the Google sync does not work. I assume I should be given an opportunity to sign in to my Google account but none appears. If I use the + button try and Create a New Calendar I am not given the option to create a Google calendar and there is no sign-in.
What am I missing?

Are these installed?


Yes, both installed on this machine.