@HolyPhoenix you can't do that without modifying code. It's not a feature that would be useful for others either to be included in core.
UNSOLVED How do I make posts in a certain category ephemeral?
I want posts in a certain category to be deleted after a period of time such as one year.
Can I do it with nodebb?
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.