I have headers for my layouts that consist of multiple buttons and objects. Oftentimes, it is the same header for many different layouts. But if I make a change to the header in one layout, I then have to go to EACH layout with the same header and duplicate the change (or copy and paste from the first layout). Is there any way to create an object that I can add to multiple layouts, such that if I make a change to the object on any of the layouts, it will reflect that change on ALL of the layouts that contain that object?

no

Ever since card windows have come out, people are using that UI tool to show a window as a sort of fly-in  menu for all layouts. This 'menu' layout has the buttons and nav tools that are global. It's a one-stop-layout for your navigation.

This gives you more pixels for your data as the menu is off screen until a user calls it up.

Card windows are such that one layout can be called by a button on many different layouts.