When previewing a page, are things supposed to work as they would once published? For example, should one be taken to the appropriate page when clicking on an item in the navbar?
If that is how it is intended to work, then it is not behaving that way currently. To me, there seems to be no difference between the editing and preview modes. When I click on a button in preview mode, it selects the button and displays its values in the inspector.
It’s different to Classic. Inside the Elements app there is only the WYSIWYG Editor! To preview your site as it appears when published, press the compass icon in the toolbar to open the site in your default browser.
We probably should have hidden that button for the beta. It’s intended to let you quickly switch between light and dark mode in the editor but it hasn’t been implemented yet.