I too use Thunderbird. I really needed the cardbook extension, and Calendar, as these both integrate well with Nextcloud (via CARDDAV and CALDAV).
I simply download the .tar.bz2 file right off the Thunderbird website. No package manager here (against all of our better judgements, admittedly)!
Once I decompress this, and move the “thunderbird” folder to my home dir, then I make a symlink to the actual thunderbird executable binary on my desktop:
ln -s /home/user/thunderbird/thunderbird /home/user/Desktop/Thunderboid
user@laptop:~$ ls -la Desktop/
lrwxrwxrwx 1 user user 44 Dec 3 21:19 Thunderboid -> /home/user/thunderbird/thunderbird
Then an Icon appears on my Ubuntu Desktop, and that’s my launcher. Thunderbird can update itself, outside the package manager:
Burger menu in the upper Right -> Help -> About Thunderbird -> Look for it saying “Thunderbird is up to date”: