Many users said after they updated to macOS Sierra 10.12, AirDrop and some other options can’t be seen sometimes. Fortunately someone has found a solution, which was tested to be effective.
If your Mac device encountered the said problem after the system was upgraded to Yosemite El Capitan, try the following solution:
1. Open the Terminal app, which is in the Utilities folder of your Applications folder.
2. Type this command in Terminal:
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -seed
3. Press Return and wait for the Terminal prompt – which ends in $ – to reappear. It may take a few minutes.
4. Quit Terminal.
Then you should see the previously missing options, such as AirDrop, Email and Share on Facebook, etc. If not, go to Apple menu > System Preferences, click Extensions, and make sure that the Markup and sharing features are turned on in the Actions and Share Menu sections.