Barcelona are in very good form. But they will play against Manchester United in the first match of the Europa League. There is no way to think of United as a weak team. Ten Hag managed to stabilize the team considerably. And we are not sure if the Barcelona team can win against United now. If Barcelona can dominate and win against Manchester United then I believe they will be able to qualify for the Europa League final.
We can't be sure how the game will turn out right now. They are about to return from a lengthy World Cup break, and not all of the teams' players will be in peak form, particularly those who did not play in the World Cup. Even though some players have been able to exercise on their own, training as a team is vastly different. Every team will have some lapses before they can be balanced on the field, in my opinion.