custom-order-status-for-woocommerce.php

<?php 
add_filter( 'woocommerce_register_shop_order_post_statuses', 'musilda_register_custom_order_status' );
function musilda_register_custom_order_status( $order_statuses ){
    
    $order_statuses['wc-custom-status'] = array(                                 
      'label'                     => _x( 'Custom Status', 'Order status', 'woocommerce' ),
      'public'                    => false,                                 
      'exclude_from_search'       => false,                                 
      'show_in_admin_all_list'    => true,                                 
      'show_in_admin_status_list' => true,                                 
      'label_count'               => _n_noop( 'Custom Status <span class="count">(%s)</span>', 'Custom Status <span class="count">(%s)</span>', 'woocommerce' ),                              
    );      
    return $order_statuses;
}

add_filter( 'wc_order_statuses', 'musilda_show_custom_order_status' );
function musilda_show_custom_order_status( $order_statuses ) {      
   $order_statuses['wc-custom-status'] = _x( 'Custom Status', 'Order status', 'woocommerce' );       
   return $order_statuses;
}
 
add_filter( 'bulk_actions-edit-shop_order', 'musilda_custom_order_status_bulk' );
function musilda_custom_order_status_bulk( $bulk_actions ) {
   
    $bulk_actions['mark_custom-status'] = 'Change status to custom status';
    return $bulk_actions;
  }