Easily the change in macOS Big Sur that you immediately miss on returning to macOS Catalina, is the new Control Center. Just as it does for the iPhone and the iPad, so Control Center now makes it easier, simpler, and faster to change key settings on the Mac.
The new Control Center in macOS Big Sur is a very convenient grouping of commonly-used functions, plus it’s now easy to drag those controls out to the menu bar. It’s just far less obvious how, or whether, you can drag them back.
The new Control Center in macOS Big Sur