Date and Time only partially visible in Big Sur
Date and time is now also Notification Center 'icon'. If it is dimmed it means that you have 'Do Not Disturb' active. To toggle between on/off DND hold ⌥ key while clicking on date/time.
If you don't like dimming then you should head to Dock &amp; Menu Bar in Preferences. On left pane select 'Do Not Disturb' and tick 'Show in menu bar' and select 'when active'. By doing this tilted half-moon icon will be displayed on Status menu if DND is active and date/time will not be dimmed.