I don't think very much should be read into that Man U victory over Liverpool. Yes, 4-0 sounds quite comprehensive, but it has to be taken in context. It's not a competitive match, and not only is it pre-season, it's early pre-season and players are still getting fit. But the biggest reason is the players they put out, Liverpool made so many substitutions, they had over 30 different players appearing in total.
https://www.bbc.co.uk/sport/football/62141591
https://www.bbc.co.uk/sport/football/62141591
This match is no more serious than the usual two-way training game inside the club. At the moment, it is not even completely known in which squas teams will start the season, so it makes no sense to pay attention to such news. However, I have already seen funny memes on this topic (the face of Klopp who releases the main players with a score of 0-3 and ends up with 0-4
).