Well the menu made in template does the 95% of the job, as you can see in the large devices version: https://snipboard.io/D5S91s.jpg the sub menu in categories, is only shown on hover. But as shared screenshot in this post, the mobile view is shown expanded which is not recommended complying with the style of this template's desktop version.
It will be a really handy template override if default collapsed categories menu is shown, pls consult the @supportguy on this issue if it can be fixed.