You can have applications that can read from the Joplin API - you can use applications like VSCode with @rxliuli's VSCode plugin to have Joplin data but entirely via VSCode and not the Joplin app. It does require Joplin itself to be running and listening.
In terms of a more offline solution there isn't anything that would stop you reading the database directly (from, if default, .config/joplin-desktop/database.sqlite
For example to get an entire list of your database you could just run
SELECT folders.title, notes.title, notes.body
FROM folders, notes
WHERE notes.parent_id = folders.id
ORDER BY folders.title, notes.title, notes.body ASC;
and that will spit out all your data (although I assume if you use encryption things won't be quite that simple...).