Best practices to author UI flow?

Hi there!
I am trying to investigate how people tend to author UI flows for games that require more than just a simple start/options/exit menu. I am looking for samples of UMG/ blueprint scripting that show complex structures and how UI scenes change between each other. For example some mobile games require popup windows, upgrade windows,etc so I am looking in a way for best practices when dealing with a complex structure of scenes for UI.

Any resources/sample projects you think could help me?