Sound icon menu bar glitch?

Hello all

I recently acquired a new MacBook. After switching it on, I quickly noticed that the volume icon was not visible in the menu bar in the upper right, where I was used to seeing it. After a little research I discovered that it had been moved into the control centre and that I could opt, within the Settings app, to have it always visible in the menu bar, or only visible "when active". The latter option would be fine, except when I choose it, it simply never appears, even when I have audio clearly running in the Music app, QuickTime, Audacity etc. What am I missing? Other Control Centre modules with the "when visible" option (eg display) also don't seem to appear when this option is chosen...