Volume icon in menu bar disappear randomly in Big Sur
I know why this happens.  Upon clicking the volume icon in the menu bar, if you misclick/misdrag anywhere but the allowable volume change slider it will interpret this as trying to rearrange the menu bar icon to another menu bar location.
My current &quot;fix&quot; is to use the open the control center menu and drag the volume back into the menu bar every time this happens.
EDIT: Seems to be fixed in MacOS 11.3