By default, the ability to switch to the classic UI from the editor has been disabled.
To re-enable the option Open in Classic UI in the Page Information menu, follow these steps.
Using CRXDE Lite, find the following node:
/libs/wcm/core/content/editor/jcr:content/content/items/content/header/items/headerbar/items/pageinfopopover/items/list/items/classicui
For example
http://localhost:4502/crx/de/index.jsp#/libs/wcm/core/content/editor/jcr%3Acontent/content/items/content/header/items/headerbar/items/pageinfopopover/items/list/items/classicui](http://localhost:4502/crx/de/index.jsp#/libs/wcm/core/content/editor/jcr%3Acontent/content/items/content/header/items/headerbar/items/pageinfopopover/items/list/items/classicui
Create an overlay using the Overlay Node option; for example:
/apps/wcm/core/content/editor/jcr:content/content/items/content/header/items/headerbar/items/pageinfopopover/items/list/items/classicui
/apps/
Add the following multi-value text property to the overlaid node:
sling:hideProperties = ["granite:hidden"]
The Open in Classic UI option is again available in the Page Information menu when editing pages.