npub1ygdpy2ptwpjln4zvnccqn5ncwwu0x3uwxh79w7rwrlmyrj9hdhzs3ychxj (npub1ygd…chxj) Would you consider posting your issue in our community support site? This is definitely not expected behavior for either service.
https://support.mozilla.org/en-US/products/thunderbird
Our account autodiscovery should pick up your calendars (regardless if it's personal Gmail or Google Workspace), and let you choose which ones to add, provided you've already gone through the oAuth process to authenticate your Gmail account.