I semi-understand the modern day managerial approach where they are sat at the sidelines, as it's mostly down to the players when they're on the pitch. Buuuuuuut, there were at least 20 or 30 occasions in that first half where Sir Alex would have been laying into that back four. The positional play on all of the goals has been shocking. I don't see anything wrong with letting the players know this whilst the game is going on, especially as there is no crowd and the players will clearly be able to hear the manager.
I disagree with the notion that managers can't impact on a game from the sidelines. They most certainly can, imo.