Idea Summary
I suggest adding an icon to the “new navigation menu entry” when creating a new page instead of going to the Shared Components every time after creating the pages,
It is preferable that it be like this one with the addition of pages when creating the application for the first time.
This should be

Like This:  

Use Case
When create a new page with a new navigation menu entry.

Preferred Solution (Optional)
I go to the Shared Component => Lists => Navigation Menus => targeted Menu => Choose Icon.