Can macOS display a key shortcut when the cursor hovers over a visible control?
There is nothing preventing the author of any specific app (Apple being the author of Pages in this case) from doing exactly what you ask for either by default or in a setting. 

Apple doesn’t have this as a standard affordable, so there’s no global switch you can run to have this enabled across multiple apps. The closest thing I can think of is the Cheat Sheet app which shows all active key shortcuts when you hold a key. It doesn’t select a button from the UI, though. 


Simplest way to capture &quot;keystroke representation&quot; to clipboard
Does OS X or Xcode have applications to manage cheat sheet/commands list?


The question covering Xcode also explains and demonstrates how to search for menu items by the help menu.