Soon a new OS -- iOS 17 -- will be coming to your iPhone, if you have one. In this article, the author laments the fact that most iPhone users haven't really grasped all the features in iOS 16, the current version. After reading the article, I've concluded I'm in that group. It would be nice if Apple made available for download a summary of new features, and how to use them, in every release of a new OS.
Having said that, some years ago the author and a friend started a new website -- https://sixcolors.com/ -- which features articles about Apple's various OSes. This might be of interest.
Jim Hamm