In the past there used to be an option in Settings->Appearance->Behavior to toggle between using the top menu bar and window-specific menubar. (Sorry, not sure exactly what they’re called.)
But in 20.04, I don’t see that option anymore. Not in settings, and not in gnome-tweaks.
This is an example of the menu that I’d like to move down from the top of the screen into the application’s window:
Can someone tell me how to do this in Ubuntu 20.04?