You should look at the summer of 2017, PSG caused a stir when they spent 222 million euros to break Neymar's contract with Barcelona. Barcelona just watched bitterly as PSG snatched Neymar from their hands. PSG believes that only Yamal has the potential to replace Kylian Mbappe. To have Yamal, PSG clearly understands that they need to have an offer that is so strong that their partner cannot refuse, enough for Barcelona to consider. In the context of not yet escaping the financial crisis, is 250 million euros enough? 250 million euros will help Barcelona do a lot of things. I believe that things can change with a lot of money. If Barcelona does not have a reasonable strategy for buying and selling players, I think Barcelona will fall into adversity again. What they need to do now is balance their finances. They need to learn how to make money from players, otherwise they will go bankrupt. Of course, Barcelona's budget is not empty yet, but it is only a matter of time.
PSG made a big mistake when they put high hopes on Mbappe, they believed that Mbappe would continue to stay at Parc des Princes with all the luxuries offered, from a high salary to other facilities. Now they have to bear the loss because they did not get any money from Mbappe departure to Real Madrid. PSG are used to signing big-money players, their bid for Yamal would again break their previous transfer record when they signed Neymar from Barcelona. The offer is very tempting, but Barcelona has no intention of releasing its young star despite receiving a high offer. PSG must look for other targets before the transfer window closes, bringing in quality players needs to be prioritized so that they can compete with other teams in the Champions League.
But it can't be said as mistake because it is only natural that PSG has high hopes for Mbappe because he is the only player that PSG has relied on the most so far in achieving victory or several championship titles.
Previously, no one knew that Mbappe would leave PSG like this because the initial goal of bringing in Mbappe was to strengthen the team and be able to win the Ligue 1 or UCL title.
Departure of players from football team is natural thing, PSG did not do anything wrong and they should not be disappointed by all of this because Mbappe departure was his own decision.
Now what PSG needs to do is to see all the potential of young players, they must focus on this and not make the mistake of spending large amounts of money on players who cannot be relied on in the future.