Its a pity that if United can still take first place in the group (in fact, for this they will just have to beat Sociedad with a score of 2-0 in the return game), then Sociedad and Barcelona will not meet each other in any way, since the draw for the play-offs takes into account countries and breeds clubs from one country. But in the later stages we will definitely see something interesting like Arsenal - Barcelona.
Manchester United can be able to top the group. It is obviously what they need to do in order to be safe in the league. Barcelona is coming to Europa and Manchester United should try to avoid them. Manchester United defence can prevent Sociedad from scoring but I am not sure Manchester United attackers will get 2 goals easily from Sociedad. Let us see what Ronaldo can do in the match, because he is obviously coming back in the match.
His return to the line-up is far from obvious to me - maybe Ten Hag will decide to punish him further and "show who's in charge here." Or Ronaldo himself will not want to play in the Europa League, I think he is ambitious enough to ignore United already and wait for the World Cup and the winter transfer window.
In addition, if Ten Hag decides that United should take first place, then he can play decisive games with the main squad, where Ronaldo is not currently included. And by the way, judging by United's recent games, I would say that Barcelona should try to avoid meeting it and not vice versa.