[apple] MacOS AirDrop icon missing or disabled

[nguyenvulong]

You could not open AirDrop from Finder
You could not add AirDrop from Finder / Settings / Sidebars

Then probably some security software screwed up your Airdrop.

To get it back, open your Terminal and paste the following

defaults write com.apple.NetworkBrowser DisableAirDrop -bool YES
defaults write com.apple.NetworkBrowser DisableAirDrop -bool NO

This will attempt to disable and re-enable AirDrop.
Check again whether you can toggle on AirDrop from the top of your screen.
If it's still not working, restart your MacBook.

Good luck.