Why are half the options missing when I right-click the taskbar on Windows 10?

Why does right-clicking the taskbar on my Windows 10 PC only show a few options now—like Toolbars and Task Manager—while things like Settings, Lock the taskbar, and Cascade windows are completely gone? Why did they disappear without me changing anything, and why does it sometimes come back after a restart only to vanish again a few hours later?

Could this be caused by a corrupted registry key, a third-party shell extension, or something a recent update changed? And is there a way to restore the full right-click menu without resetting the entire taskbar configuration?