/** Show Primary Category for All Posts on Post Block widget */
function jkit_show_primary_category_on_post_block_for_all_post( $category_id, $post_id ) {
	if ( ! empty( $category_id ) ) {
		return $category_id;
	}

	$categories = array_slice( get_the_category( $post_id ), 0, 1 );

	if ( empty( $categories ) ) {
		return null;
	}

	$category    = array_shift( $categories );
	$category_id = $category->term_id;

	return $category_id;
}
add_filter( 'jeg_primary_category', 'jkit_show_primary_category_on_post_block_for_all_post', 10, 2 );