Hello Newbie214,
Thanks for using the Apple Support Communities. We understand that you have concerns regarding the black rectangle surrounding the Apple Menu icon in the upper left corner of your screen. Is it causing any issues with your device or have you noticed this occurring which other applications or toolbars? Since first noticing it, have you tried restarting your Mac?
Log out, sleep, wake, restart, or shut down your Mac
When did you notice this appear? Was it after a recent macOS or app update? If you adjust your device wallpaper or screen resolution, does it persist?
Customize the desktop picture on your Mac
Using a Retina display- Changing the resolution of your display
Please let us know how goes if you decide to make any adjustments to the display or wallpaper.
Best regards.