I do a lot of UI/UX design in Illustrator. Often, I find myself needing to create different screens with slightly different elements (e.g. an open hamburger menu/a modal. something like below). I've been resorting to simply copying the whole artboard with all elements, however drawback is that it doesn't update if I change the first screen, and creates a ton of duplicate items. What's the best solution for this?
Create your first screen, and drag the art to the Symbols Panel. -- Or drag the individual elements to the symbols panel. Symbols act sort of like "master elements". You can then edit the symbol once, and see all other instances update.
More about symbols here: https://helpx.adobe.com/illustrator/using/symbols.html