Apple is not a company known for sharing information since they are secretive by nature. I cannot count how many times I find out about a new way to do something (especially on the iPhone) that was not even well covered on the review sites. For macOS or iOS information, I tend to read at least one review describing all the new changes to the OS (additions, changes, and deletions of features) which helps a bit. I usually like the articles on the arstechnica.com website as they tend to provide a good detailed overview and some technical details of any new features, although they were a bit lacking on properly describing the new Stage Master feature in macOS 13.x Ventura.
Or you can watch Apple's launch event when announcing the new operating systems or products.