I’m not sure when this started, but .ICS files no longer open in Outlook 2016 on Windows 10 for me. Instead, they open in the unremovable Calendar app which, of course, isn’t something I care to use. Of course there is no place to set a default calendar app and I can’t even associate the .ics file extension with Outlook. When I try, my only options are to associate with the Calendar app or to find another app in the store. Good grief. Any ideas?