Still working great in April 2024

Works without any issues for me in WordPress 6.4.4

I added some custom backend CSS (via the Code Snippets plugin) to style it with the eye/visibility icons and semi opaque descriptions for a more intuitive user-experience:

add_action('admin_head', 'custom_admin_css');
function custom_admin_css() {
  echo '<style>
	/*-------/ Plugin: Admin Collapse Subpages /-------*/
	body.wp-admin .column-primary .expand_link a:before {content: "\f530"; opacity: 0.85;}
	body.wp-admin .column-primary .expand_link a.minus:before {content: "\f177"; opacity: 0.3;}
	body.wp-admin .column-primary .expand_link a:after {
    	content: "Subpages hidden";
		position: absolute;
		font-family: sans-serif;
		font-size: 10px;
		height: 12px;
		opacity: 0.85;
		margin: 3px 0 0 5px;}
	body.wp-admin .column-primary .expand_link a.minus:after {content: "Click to hide subpages"; opacity: 0.3;}
	body.wp-admin .column-primary .expand_link a:hover:before,body.wp-admin .column-primary .expand_link a:hover:after {opacity: 1;}
	body.wp-admin .column-primary .expand_link a.minus:hover:before,body.wp-admin .column-primary .expand_link a.minus:hover:after {opacity: 0.6;}
  </style>';
}