This might not be related to your post but I would like reply here for reference as well. I think iOS16.1 also blocks access to calendar database as well.
My widget app displays info from calendar and it stops working correctly since iOS16.1. It happens when the widget try to refresh the timeline (thus need to access calendar database). If I refresh the widget from within my app, the widget can access calendar database correctly.
I have also found a post on Reddit regarding this issue - https://www.reddit.com/r/iOSBeta/comments/xgship/ios_161_b1_3rd_party_calendar_widgets_not_working/
Hope Apple will fix this soon.