TB stores its local address books in the profile folder on your computer, but it can also include (sync with) contacts that are stored in cloud accounts like Google, iCloud, outlook.com etc. Providers like Google that support CardDAV can be added to Address Book directly, while others require an add-on like TbSync.

thanks for replying. i'm a thunderbird newbie. your answer sounds like no, there's no backup protection. my next questions are: how do i backup those files? can i do it automatically? is there an add-on? i'm using windows 11 and just downloaded the latest tb version.

You can backup all your data and settings by copying the profile folder to a safe location. Help/More Troubleshooting, about:profiles, shows the profile location.

Address books can be backed up by exporting them to LDIF files (Address Book, Tools/Export, Save as type:LDIF).