Comment 57 for bug 1850651

In 'Options' > 'Update':
I have selected 'Check for updates, but let me choose whether to install them'
Thunderbird does as expected. I see a pop up saying there is a new update and asking if I want to update.

If you have the 'Automatically install updates' option selected - note this is selected by default - then Thunderbird will auto update at the appropriate time. You would then prompted to restart.

What do you mean by 'this new (broken) version' ? Do you only mean you are using addons created by various users/authors and those addons are not working ?
If yes, then Thunderbird is not broken. You may discover many addons can be updated / some are in the pipline / some issues can be fixed by alternative ways. Suggest you ask a question in the Support Forum to see if something can be done.

Or
are you refering to the bug discussed in this bug report which claims the update has fixed?
Are you using the up to date addon: Provider for Google Calendar version 68.0
What issue are you experiencing with the Imap gmail account?