Sharing Notes on Catalina
Follow these steps if the issue occurred immediately after upgrading 


Open the Terminal app, which is in the Utilities folder of your Applications folder. 
Type this command in Terminal:

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -seed
Press Return and wait for the Terminal prompt—which ends in $—to reappear. It may take a few minutes.
Quit Terminal. 


And later 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 too after running the above command.