How can I show seconds on macOS BigSur's menu bar clock?
On macOS older than Big Sur, the System preferences can be configured to show seconds on the menu bar clock:


Apple has changed up the menu bar on Big Sur specifically and people have opinions about that for certain. There is no seconds display that’s easily enabled on 11.3 and below.

How do you remove the time from the menu bar in Big Sur
macOS Big Sur - how to show exact time when clicking on analog clock in the menu bar?