[Evolution] Gmail: stuck logging in

[Keith Barber <keith keith barber name>]

I've just added a gmail account to my Evolution setup; both have
existed for some time and worked well, this is the first time I've
tried to connect them.

Initial problems (an Oauth2 loop) led me to the thread "Re: [Evolution]
Gmail Oauth2 loop" from December last year; I followed Milan's advice
(thank you for that, worked fine) but now I'm stuck again. I try to log
in to the gmail account, I'm asked for the password each time and,
having allowed google to trust Evolution I get this message: 
"Failed to open folder.
The reported error was “Authentication password not available”.

All my other accounts seem to be working perfectly.

Following update I am running Evolution 3.44.3 under Ubuntu 20.04.4

Any help would be appreciated (including pointing out something obvious
I'm missing - I'm at the beginner end of the computer expert spectrum).
-- 
Best wishes
Keith Barber
(He/him)