Rated 5 out of 5 stars

It turns out Thunderbird already supports Google Calendar by default:
https://support.mozilla.org/en-US/kb/using-lightning-google-calendar

No need for any add-ons!

I followed the steps from the How To and added my calendar without any issues.

It is now natively supported and smoothly syncing with Google Calendar!

This review is for a previous version of the add-on (128.5.2).