If you do not have a specific - and very good - argument / reason to need an old Thunderbird:
Then do install the one provided by sudo apt install thunderbird
(type that in a Terminal / Shell / at the Bash prompt).
This will (currently) install version 91.8.1 if I'm not mistaken, it will also be auto-updated when new versions or updates become available; depending only on how you set the update options [1].
Note: I would not expect it to cause any problems, even if using it for any files you have saved.
Note2: As a beginner Ubuntu / Mate user you will have the least problems if you restrict software installs to be via apt
(as above), System software
or any other means that uses ppa
:s or *.deb files. Opinion: snap-package -installs seems flaky IMO, that might have changed after I stopped using them though.
And one more opinion of mine; Everything else is for advanced and experienced Linux users.
[1] hit the Win-key, type updater
and Software updates
will appear, click on it, it checks for updates and then; click Settings ...
to set options. (Assumption: Mate works the same as "Ubuntu")