Yes, that's known as global application menu (not enabled by default). It's not the most discoverable feature, but it's working great once set up. (For reference, just add the widget to your panel and then make sure to restart plasma for it to take effect).

Yes, this was mandatory for me. It's the reason I switched from GNOME to KDE originally, GNOME broke the global menu bar.

You can recreate the layout almost perfectly. Don't try to theme it as macOS, just get the UI components in the right places using the widgets it comes with.

KDE has a global menu bar widget. Unfortunately not all applications work with it.