Barcelona and Xavi are aiming to win the La Liga title and the Europa League title. On the other hand, Ten Hag and Manchester United's main goals are to qualify for the Champions League and the Europa League title. Arsenal will also continue to fight for the Europa League title. It is difficult to predict which team will win the title. But every team has a good instinct to win the title. United and Barcelona's performances have been somewhat unstable, but both have strong squads. But both the teams have enough time to organize themselves and strengthen the team.
In fact, it is very difficult to say now what priorities Arsenal, Manchester United and Barcelona will have in the EL. It is possible that Arsenal and Barcelona will have to focus on their championships and since I think that they have already secured a place in the Champions League for next season, the EL may not be their main priority tournament, and they may sacrifice it if the situation requires it.
Yes it is a situation that will drain them to do their best in these 2 competitions. Their main objective is definitely in the League, but when they get a good chance in the Europa League then I'm sure they will make the most of it and won't miss the chance that comes their way. Arsenal and Barcelona are in a good situation in the league table, they will definitely try to prioritize that first. The term if all they can get why not.