On iOS 13 devices I assume the setting 'Siri Suggestions' does the same thing. On pre-iOS 13 devices I also unchecked the 'Siri Found in Apps' option under the 'Other' category. Yeah, I ended up stepping through all the steps outlined above for Apple Calendar and a separate set of steps for Google Calendar. Wow, is it just a coincidence I just started getting these calendar spam invitations TODAY? I got the same one claiming a free iPhone X on both my Apple Calendar and Google Calendar.
