I am unable to access Menu Bar on external monitors connected to iMac post macOS Update

Hi folks. I have no idea what has happened, but this week the top Menu Bar with the Apple icon, which used to appear on both of my screens (iMac and external monitor), now only appears on my iMac, or, if I go into System Settings, whichever display I arrange.

I don't use Launchpad, Spaces, Mission Control or Full Screen for any of my apps, so I'm just curious whether an update has removed that functionality. If so, why? And can I have it back, please?

There is a horrible gap above my applications on the external, and it irks my OCD somewhat.

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