That would not make sense from a functional point of view, a user that belongs to that group could simply log out and see the category anyway.
From a technical point of view it is impossible, if a category is accessible to everyone, Discourse sets the read_restricted flag to false and all access mechanisms are bypassed.
From this plugins perspective, the closest you can get is NOT excluded_group (which is the same as trust_level_0 AND NOT excluded_group). But an anonymous user cannot be in a group, so no.