Review for Google Calendar Tab by cakira
Rated 5 out of 5 stars
It works with Thunderbird 128.0.1esr, but it took me a while to find the button.
To access it, go to the email tab, and you'll see the Google Calendar icon in the upper right corner of the window.
I plan to use this extension because my company uses Google Workspace, and when I add the calendar in Thunderbird, it only shows the free/busy status due to company policy. There might be a way to add the corporate calendar natively in Thunderbird (my Alexa can see my calendar, so why can't Thunderbird?), but I haven't found a solution yet.
To create your own collections, you must have a Mozilla Add-ons account.