Since Ferguson left the club Manchester United have not been a club recognized with that level of patience with managers. They have been known to be strict and inpatient with managers just like Chelsea believing the managers were the problem why the club has struggled for years to maintain stability in their performance at all levels ignoring the fact that the problem traces up to the top hierarchy too.
That era ended with Alex Ferguson and Arsene Wenger many years ago, and nowadays you can not find such patience given to a head coach in many years. The world changed, football changed, club owners changed, monetary power and effects on football club development strategies changed. Nothing is the same like 20 years ago, and Manchester United are like all other clubs, no longer have too much patience for their head coaches.
They tried it with Solskajer then Ten Hag, but failed and they will probably change their strategy and approach again. There are clubs that don't need to work with a coach for 10 years or longer but still succeed, so actual main problems in Manchester United are something else, not only patience.