I've been using caldav and carddav in Thunderbird for over a year, and I don't believe I installed any plugins for it - I'm tempted to say yes? What prompts the question?
Last time I tried I had to install external address book extension and calendar and it did not integrate that well (auto completion not working properly...).
So, i just nuked and paved my current machine, and just before i did i know for a fact that caldav worked flawlessly on Thunderbird version 91...And, CardDav? Meh, not so great. And neither caldav nor carddav required me to add/install any extensions; so, really, i see it as progress.
As soon as i'm done with other elements of my new machine install here, i will see how a newer version of thunderbird handles caldav and cardav...But, my point is, at least caldav used to work really, really nicely and smoothly on older versions of thunderbird. (Caveat: this is with Zoho as calendar/caldav provider...so no idea about trying to use Google calendar or other cal. providers.)
