Need help with Custom Taxonomy + Custom Post Type

why it not working

Because your post type’s permalink structure (which defaults to our-work/<post name/slug>) does not contain the category.

So if you want the permalink structure for your post type (our-work) be our-work/<category>/<post name/slug>, here’s one way that works in WordPress 5.6 & 5.5, but uses just one of the post categories:

1. Add the <category> part to the post type’s rewrite slug — here we’re using %projects% as the category placeholder, but you can use other tag like %project_cats%:

   register_post_type( 'our-work', array(
       'rewrite' => array( 'slug' => 'our-work/%projects%' ),
       // your other args
   ) );
   

2. Use the post_type_link hook to replace the above part (i.e. %projects%) with the actual category slug:

   add_filter( 'post_type_link', 'my_post_type_link', 10, 2 );
   function my_post_type_link( $post_link, $post ) {
       if ( $post && 'our-work' === $post->post_type ) {
           // Get all the "projects" terms assigned to the post.
           $terms = get_the_terms( $post, 'projects' );
   
           // But use only the first term ($terms[0]) which is normally the most recent
           // term assigned to the post. So if you assigned it the terms Foo and later
           // Bar, $terms[0] would be the Bar term.
           $post_link = str_replace( '%projects%', $terms[0]->slug, $post_link );
       }
   
       return $post_link;
   }
   

That’s all, and be sure to flush the rewrite rules (just visit the permalink settings page).