I liken Manchester United to Sevilla this season for now. I mean you know what Sevilla did last season. They were horrible in the La Liga most of the time. But on one hand their performance in the Europa League was marvelous after a point. They even won the Europa League title while not doing well in the La Liga.
I don't say that Manchester United will win the Champions League of course.

But despite their poor effort in the Premier League so far their performance in the Champions League against Bayern Munich was really promising. It seems like they can concentrate on that tournament more currently.
Manchester United always have a chance to come out of third place in the EL and win this tournament to become like Sevilla.

In the match against Bayern. they almoust bounced back well, but this became possible largely because Bayern was too carried away with the attack and forgot a little about defense, and Bayern doesn’t have the best goalkeeper in the goal right now, so Bayern concedes a lot.
I think Manchester United will not be as strong as we imagine in the UCL because they have difficulty maintaining their best form. As you said it is possible that they will come out of third place and play in the EL which makes us not really expect that to be a reality for them this season. I think Manchester United still has high hopes of qualifying for the round of 16 because there are still many matches that they can use as best as possible to improve their performance.
Previously I believed that in Group A only Bayern Munich and Manchester United were really strong, so I am still quite confident that Manchester United can overcome their problem of inconsistency in the UCL. The match against Galatasaray is one of the final results that I want to see them get 3 points in this match. If this is successful, they will have an even greater chance of qualifying for the round of 16.