In Mac OS you can record video from your iPhone in Quicktime (screen record), but you can't stream the video from the camera. It would be really great if Apple allowed that.
edit: I just found a free app by the same developer which allows just that! Yay
I feel that the ideal situation is your streaming platform offering a first-party app on iOS. I believe YouTube and Facebook already have this, but Twitch doesn't.
edit: I just found a free app by the same developer which allows just that! Yay
https://apps.apple.com/us/app/telecast-camera-usb-webcam/id1...