create post type with sub menues

create-post-type.php

<?php

/**
 * circulars post type registration and category registration.
 * @since 1.0.0
 */

function custom_post_type() {
	$labels = array(
		'name'               => 'Circulars',
		'singular_name'      => 'Circular',
		'add_new'            => 'Add New',
		'add_new_item'       => 'Add New Circular',
		'edit_item'          => 'Edit Circular',
		'new_item'           => 'New Circular',
		'view_item'          => 'View Circular',
		'search_items'       => 'Search Circulars',
		'not_found'          => 'No circulars found',
		'not_found_in_trash' => 'No circulars found in Trash',
		'parent_item_colon'  => '',
		'menu_name'          => 'Circulars',
	);
	$args   = array(
		'labels'             => $labels,
		'public'             => true,
		'publicly_queryable' => true,
		'show_ui'            => true,
		'show_in_menu'       => true,
		'query_var'          => true,
		'rewrite'            => array( 'slug' => 'circular' ),
		'capability_type'    => 'post',
		'has_archive'        => true,
		'hierarchical'       => false,
		'menu_position'      => 10,
		'menu_icon'          => 'dashicons-media-document',
		'show_in_rest'       => true,
		'supports'           => array( 'title', 'editor', 'author', 'thumbnail' ),
	);
	register_post_type( 'circular', $args );

	// Add categories taxonomy to circulars
	$taxonomy_labels = array(
		'name'                       => 'Circular Types',
		'singular_name'              => 'Circular Type',
		'search_items'               => 'Search Circular Types',
		'popular_items'              => 'Popular Circular Types',
		'all_items'                  => 'All Circular Types',
		'parent_item'                => 'Parent Circular Type',
		'parent_item_colon'          => 'Parent Circular Type:',
		'edit_item'                  => 'Edit Circular Type',
		'update_item'                => 'Update Circular Type',
		'add_new_item'               => 'Add New Circular Type',
		'new_item_name'              => 'New Circular Type Name',
		'separate_items_with_commas' => 'Separate circular types with commas',
		'add_or_remove_items'        => 'Add or remove circular types',
		'choose_from_most_used'      => 'Choose from the most used circular types',
		'not_found'                  => 'No circular types found',
		'menu_name'                  => 'Circular Types',
	);
	$taxonomy_args   = array(
		'hierarchical'      => true,
		'labels'            => $taxonomy_labels,
		'show_ui'           => true,
		'show_admin_column' => true,
		'query_var'         => true,
		'rewrite'           => array( 'slug' => 'circular-type' ),
	);
	register_taxonomy( 'circular_type', 'circular', $taxonomy_args );
}

// Add submenu page for uploading circular documents
function add_custom_submenu_page() {
	if (current_user_can('manage_options')) {
		add_submenu_page(
			'edit.php?post_type=circular',
			'Upload Circulars',
			'Upload Circulars',
			'manage_options',
			'upload-circulars',
			'upload_circulars_callback'
		);
	}
}


function upload_circulars_callback() {
    // Callback function for the "Upload Documents" submenu page
    // Add your HTML and form handling logic here
	require_once trailingslashit( get_stylesheet_directory() ).'inc/Circulars/views/view-upload.php';

}

add_action( 'init', 'custom_post_type' );
add_action( 'admin_menu', 'add_custom_submenu_page' );