They spent the whole season without their centre-forward and reiterated that they were a great team, first winning the La Liga championship and then the Champions League. There was only one cup missing, I think, with the Mbappe transfer, they became candidates again for all the trophies that can be won next year.
Xavi has left the Barcelona side and it should only be a matter of time before the team announces new transfers. Yes, first of all, Barcelona needs new players to organize its fragile defensive line.
Mbappe joining Real Madrid will of course make them much stronger next season, even Real Madrid this season is without a center forward as a replacement for Benzema, but they managed to be successful by winning two prestigious trophies. I think the competition in Laliga next season will not be too interesting because Real Madrid is much stronger and Barcelona certainly won't be strong enough to prevent Real Madrid from becoming champions. It's not that I underestimate Barcelona, but this season alone, Barcelona is quite far behind in points and that marks a major setback in the competition between the two.
For Mbappe, of course, he has officially become a Real Madrid player because Fabrizio announced it on Twitter. But for that we just wait for the official announcement from the Real Madrid team. I think the reception for Mbappe as Real Madrid newest player will certainly be quite enthusiastic because he is one of the quality strikers who will be able to make Real Madrid even stronger.