Register WordPress custom post type and tax, where single items view is redirected to 404 page but item archives are still accessible.

thz_cpt_items_single_view_redirect.php

<?php

// post type
function cpt_items_register() {

	$cpt_labels = array(
		'name'                  => _x( 'Items', 'Post Type General Name', '{domain}' ),
		'singular_name'         => _x( 'Item', 'Post Type Singular Name', '{domain}' ),
		'menu_name'             => esc_html__( 'Items', '{domain}' ),
		'name_admin_bar'        => esc_html__( 'Page Block', '{domain}' ),
		'archives'              => esc_html__( 'Item Archives', '{domain}' ),
		'attributes'            => esc_html__( 'Item Attributes', '{domain}' ),
		'parent_item_colon'     => esc_html__( 'Parent Item:', '{domain}' ),
		'all_items'             => esc_html__( 'All Items', '{domain}' ),
		'add_new_item'          => esc_html__( 'Add New Item', '{domain}' ),
		'add_new'               => esc_html__( 'Add New Item', '{domain}' ),
		'new_item'              => esc_html__( 'New Item', '{domain}' ),
		'edit_item'             => esc_html__( 'Edit Item', '{domain}' ),
		'update_item'           => esc_html__( 'Update Item', '{domain}' ),
		'view_item'             => esc_html__( 'View Item', '{domain}' ),
		'view_items'            => esc_html__( 'View Items', '{domain}' ),
		'search_items'          => esc_html__( 'Search Items', '{domain}' ),
		'not_found'             => esc_html__( 'Not found', '{domain}' ),
		'not_found_in_trash'    => esc_html__( 'Not found in Trash', '{domain}' ),
		'items_list'            => esc_html__( 'Blocks list', '{domain}' ),
		'items_list_navigation' => esc_html__( 'Blocks list navigation', '{domain}' ),
		'filter_items_list'     => esc_html__( 'Filter items list', '{domain}' ),
		'featured_image'        => esc_html__( 'Featured Image', '{domain}' ),
		'set_featured_image'    => esc_html__( 'Set featured image', '{domain}' ),
		'remove_featured_image' => esc_html__( 'Remove featured image', '{domain}' ),
		'use_featured_image'    => esc_html__( 'Use as featured image', '{domain}' ),
	);


	$cpt_args = array(
		'label'                 => esc_html__( 'Item', '{domain}' ),
		'description'           => esc_html__( 'Item description', '{domain}' ),
		'labels'                => $cpt_labels,
		'supports'              => array( 'title','editor','excerpt','revisions', 'author','thumbnail'),
		'hierarchical'          => true,
		'public'                => true,
		'show_ui'               => true,
		'show_in_menu'          => true,
		'show_in_admin_bar'     => true,
		'show_in_nav_menus'     => false,
		'has_archive'           => 'items',     
		'exclude_from_search'   => false,
		'publicly_queryable'    => true,
		'capability_type'       => 'post',
		'query_var'             => false // disables item single view and redirects it to 404 page

	);
	
	register_post_type( 'item', $cpt_args );

}

add_action( 'init', 'cpt_items_register', 0 );


// tax
function cpt_items_tax_register() {
	
	$ctx_labels = array(
		'name'                          => _x( 'Items Categories','taxonomy general name', '{domain}' ),
		'singular_name'                 => _x( 'Item Category','taxonomy singular name', '{domain}' ),
		'search_items'                  => esc_html__( 'Search Categories', '{domain}' ),
		'popular_items'                 => esc_html__( 'Popular Categories', '{domain}' ),
		'all_items'                     => esc_html__( 'All Categories', '{domain}' ),
		'parent_item'                   => esc_html__( 'Parent Category', '{domain}' ),
		'edit_item'                     => esc_html__( 'Edit Category', '{domain}' ),
		'update_item'                   => esc_html__( 'Update Category', '{domain}' ),
		'add_new_item'                  => esc_html__( 'Add New Category', '{domain}' ),
		'new_item_name'                 => esc_html__( 'New Category', '{domain}' ),
		'separate_items_with_commas'    => esc_html__( 'Separate categories with commas', '{domain}' ),
		'add_or_remove_items'           => esc_html__( 'Add or remove categories', '{domain}' ),
		'choose_from_most_used'         => esc_html__( 'Choose from most used categories', '{domain}' )
	);

	$rewrite = array( 
		'slug' => 'items', 
		'hierarchical' => true, 
		'with_front' => false 
	);

	$ctx_args = array(
		'label'                         => esc_html__('Items Categories', '{domain}' ),
		'labels'                        => $ctx_labels,
		'public'                        => true,
		'hierarchical'                  => true,
		'show_ui'                       => true,
		'show_in_nav_menus'             => true,
		'show_admin_column' 			=> true,
		'rewrite'                       => $rewrite,
	);	
	
	register_taxonomy( 'items', 'item', $ctx_args );
}

add_action('init', 'cpt_items_tax_register');