Vertical menu system works differently. If you’ve imported the demo content then you’ll notice in your pages there are 2 home pages where “Home Two” is the homepage designed with vertical navigation. Still if you want to use on a blank page then what you’ve to do is set the navigation system into your edit page. Check the screenshot: https://prnt.sc/qypvn7
Also there’s option to set it global in theme option. Let me know if this helps you or not.