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Apple iPhone 15 relegated to USB 2.0 unless you buy the Pro
(www.pcgamer.com)
This is a most excellent place for technology news and articles.
The pro can stream a 4k60 ProRes video to an external drive via the usbc port. Idk what kind of bandwidth that uses. But should give some clue as to the actual speed capable with the port.
Also, onboard storage is limited to 4k30 ProRes, possibly indicating the speed of built in storage.