Menu Bar- clock-Big Sur I am successfully using 'defaults write com.apple.menuextra.clock IsAnalog -bool true' to replace to a smaller icon the Apple clock in Big Sur.
Is there a code to revert to Apple's clock if ever required?
Deleting a key will set it back to its default value.
defaults delete com.apple.menuextra.clock IsAnalog

However, you don't even need to delve into defaults to make this change, to or from analog — it's in the UI: System Preferences → Dock &amp; Menu Bar → Clock → Time Options.