There are multiple ways how you can hide pages or items in Domino Leap.
Hidding Pages 
A no-code way how to hide pages from navigation is to use one of the following options:
- use stage visibility rules
- use item-level rules
A low-code way is to use repective methot of the Form object:
- form.removePageFromNavigation(pageId)
- form.restorePageNavigation(pageId)
You can copy pageId from Editor, call page.getId() to get id of the current page or find a page using form.getPageIds()
Hidding Items 
Hidding items works in a similar way. You can hide an item:
- by stage visibility rule
- by item display rule
- by JavaScript
To hide an iten, call item.SetVisible(false), to unhide it call item.SetVisible(true).
Please note that if an item is hidden by a rule, stage, or because its parent item is hidden, you cannot make it visible using JavaScript methods.