Want to confirm that the offline method still works on this one, as of today Dec 30, 2019.
Method is to go to settings -> general -> network settings -> go offline, forget the network connection if you connect to wifi, then hard restart your xbox (hitting the xbox button on your controller then restart works). When your xbox reboots, go back into settings -> system -> time, change the date to the 14th (month shouldn't matter but I picked one in the past). Load up MCC and get into a game of Reach. I loaded up the first campaign mission but anything should work. Let it play for about a minute, then hit the xbox button on your controller, go back into network settings and reconnect, setting your wifi back up if necessary, then get back into MCC. The achievement popped after 2-3 mins of playing.