Regarding question: Converting a comment to an answer (again) and the comment following it:
Is there a list of iOS (or other) app functions that are not available on the SE web site?
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No, there is no such thing.
The closest you get now is querying for all questions that have three tags: ios-app feature-request and status-completed. If you combine those, you will see most features requested by users. Features introduced by the team can't be found that way.
Here is the list of posts matching that filter.