Came across your post, while trying to identify when an app is using this key.
You probably found this by now, but if not, here you go: https://developer.apple.com/documentation/bundleresources/information_property_list/nsupdatesecuritypolicy
It suggests just letting Xcode do the work for you (using the Info tab) in terms of placement and population of the dictionary.
Hope it all works out for your app.
inNZyet
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