Looking to restrict a user to post only in 1 category

I’ve got some users who barely know anything, so I can’t rely on the fact that they would post in the right categories. Wondering how to make it so that I can set user #1 to only be able to post in a single category, and user #2 in a different category, etc, etc. If this needs to be a plugin, is there one? Is there something I can put in functions.php?