update auto primary category with FSV Frankfurt

add_action(
    'jnews_single_post_begin',
    function () {
        $parimary_cat = get_post_meta( get_the_ID(), 'jnews_primary_category', true );
        if ( empty( $parimary_cat['ID'] ) ) {
            $categories = get_the_category( get_the_ID() );
            foreach ( $categories as $category ) {
                //change the gaming with your category FSV Frankfurt slug
                if ( 'gaming' === $category->slug ) {
                    update_post_meta( get_the_ID(), 'jnews_primary_category', array( 'id' => (int) $category->cat_ID ) );
                }
            }
        }
    }
);