Author restriction to… category?

If you’re needing to do this on a per user basis, you can use Role Scoper: https://www.ads-software.com/extend/plugins/role-scoper/

If you only need to do this for a particular role, then you can probably use: https://www.ads-software.com/extend/plugins/restrict-categories/

Role Scoper can be a bit overwhelming the first time you dive in. It looks like this individual has done what you’re looking for specifically: https://agapetry.net/forum/role-scoper-case-studies/user-role-for-specific-post-category/page-1/post-2900/