Not avaiable out of the box, but you can use something like https://github.com/julianlam/nodebb-plugin-archiver or modify it to delete the topics instead of locking.
Unsolved Error on export user's post
Hi, how can admin export users's posts?
but I have this error
/api/user/xxxxx/export/posts Not Found
You seem to have stumbled upon a page that does not exist. Return to the home page.
Thanks in advance