"Displays have separate Spaces" seems to hide the menubar, break full-screen apps?

This is the strangest thing. If in Mission Control, I uncheck "Displays have separate Spaces", it results in the menubar only showing on the primary display, despite the presence of the menubar having little to do with separate spaces.

This is in addition to the fact that you can't put two full-screen apps next to each other with the option checked; if you full-screen an app, your mother monitor(s) just go black.

What gives? Is there a workaround for either bug? 😿