I was able to resolve the issue!
`
Restart your machine and hold Cmd + R until you hear the chime. You'll enter recovery mode.
Once there open a terminal and type the following:
csrutil disable
This will disable the System Integrity Protection. After that just restart the machine.
All the widgets should be back.
Repeat the process again but this time type in the Terminal:
csrutil enable
And restart. You should be good to go now.`
Sharing with any extension did nothing for me except cause the share menu to become unresponsive. Also copy and paste stopped working in whatever application I tried to share from. Today I noticed that the "Today" view in Notification Center was empty. Found the solution here : Notification Center Missing All Widgets?
And surprisingly it also fixed the share extension! 🙂