How to uninstall the taskbar overflow menu

As per your screenshot, I assume you want to hide build information Desktop watermark.

Try these steps:

Open Registry Editor using regedit command.

You can go to following registry location:

HKEY_CURRENT_USER\Control Panel\Desktop

In the right pane, set PaintDesktopVersion to 0.

Let us know if this helps!

P.S. If you're new to registry, create System Restore point before above steps.