I tried that one and I get /Library/Apple/System/Library/LaunchDaemons/com.apple.rpmuxd.plist: service already loaded Load failed: 37: Operation already in progress :(

Same here on iOS 14.4, macOS 11.1 and Xcode 12.4 When the UDID is copy pasted with all caps I get Starting device <My UDID> [FAILED] For a laugh I tried changing the letters to lower-case and get no stdout, also tried -l and -L after each and "Could not get list of devices" I'm just starting out on Apple development so I might've missed something though... Edit: I've tried with and without sudo