Cannot open files from iCloud drive on Mac but they open on iOS devices
Solution 1:
Had this issue - Opened System Preferences - iCloud - UNselect iCloud Drive (confirm removing local files) - reboot. Login again - do the reverse: System Pref - iCloud - Select iCloud Drive. Have a touch of patiences when you try to open files as that takes a few minutes to get everything back in order. Worked perfectly for me.