Irritating popup re Google Calendar

I'm frequently being prompted by a popup (initiated by Thunderbird?) to input my password for Google Calendar, even though I've removed my Gmail account (with its data) from ThunderBird though I haven't deleted the Gmail a/c as I use that a/c for my Android phone's Gmail a/c : interestingly, the popup then asks again presumably due to rejecting my correct password! Any ideas on how to stop this popup appearing or to get the password accepted by the popup? NB Ubuntu 20.04, Thunderbird 91.7.0