I think it is purely a desire for him to go and not because of competition or anything else because Lionel Messi has won every title in his football career. messi is often associated with mbappe and they are often compared unfairly in comparing the qualities of the two. I even think it's lucky for Mbappe to have the experience of playing with a football legend in mastering all the ways and forms in terms of the qualities that Lionel Messi has.
Messi looks to obsessed with his ambition to win another and last Champions League in his career. Beyond that, he has nothing more to want and it is not bad if he leaves Europe and move to Saudi Arabia to enjoy very last seasons in his career but be able to fill up his pocket with hundreds of million dollar.
I think Barcelona will make every effort to repatriate Lionel Messi, especially the option of selling players that they will carry out in the transfer season window to balance their expenses.
Chance to win Champions League with Barcelona is small and they are not able to pay high salary for Messi. It pluses with bad treatment they gave to Messi two years ago, they will not have chance to convince him to return.
Maybe you are right, Messi is really targeting the Champions League trophy for the end of his career as a soccer player. I will not feel pessimistic if he will succeed in next season with a good record he should be able to do with a club that has strong strength and that is team manchester city. but I don't think he will betray Barcelona even though he was quite disappointed two years ago for the treatment he received.
Xavi has tempted Messi to accept the offer to return to Barcelona. Moreover, all Barcelona players really hope that Lionel Messi can return to Barcelona, especially Lewandowski, who has said that it would be quite special if he played in the same team as Messi.