Google Calendar "Settings and sharing" says only "Settings" and not "Sharing"

 That is, the "sharing" options are completely missing.

I had 1 calendar of several like this.  I never could figure out how to fix it; I had to create a new one, move events from the broken one to the new one, and delete the broken one.

Yes, it's a pain, but there wasn't anything else for it.

Note that - depending on your calendar app - you may have to go into your phone Calendar app settings to make the new calendar actually visible!