I am trying to model my “add comment” interface with what you see in the diagram below. However, I was unable to find such a UI element in the XCode library.
Is this a customized UI element? Or can I find a UI with the same look and feel as what you see in the diagram?

You can approximate it using a UIImageView (the silver gray background) and a UITextView on top of it which has a proper cornerRadius set. You’ll need to:
in order to be able to set the cornerRadius property of the UITextView like this: