Garmin Express can't find my fenix 6 Sapphire Pro

I have tried on both Mac OS and Windows to connect my fenix 6. The watch charges through the computers, but Garmin Express will not find the device. The device also not show up in Finder or the Windows equivalent. I have reinstalled Express several times, bought a new data cable (£33!!) from Garmin, rebooted the computer and restarted the watch. It means I cannot sync any routes or get updates. Help!