UCL competition and League 1 competition are not the same. UCL championship is PSG's biggest dream. To win that cup, they spent a lot of money to create a triple offensive line with Messi, Neymar and Mbappe. Only Mbappe remained today, but they still managed to qualify. They will play important matches for the UCL and I think advancing to the next round is more important for them than League 1 matches.
Since PSG became a rich team in France they have been able to get every trophy in Ligue 1, and even it seems that there is no season for them with not winning at least one trophy in the domestic league so far, PSG's journey in Ligue 1 certainly will not a team be able to prevent them from winning the title and that's why I think maybe if PSG only target the Ligue 1 trophy they will not have to spend a lot of money so far.
The Champions League trophy is the target of all teams, both big and small in Europe, and all teams dare to spend all their financial capabilities just to compete for the big ear trophy so far, including PSG, so far it is no longer counted how much money has been spent by PSG to get their first Champions League trophy, including by bringing Messi and Neymar at that time, with the MNM trio not doubting PSG could win trophies but in fact they continue to fail and now maybe they will continue to extend the record of failure because they only hope for Mbappe, I personally do not see if Mbappe will realize PSG's dream at this time because after all the PSG squad when having MNM up front is still much more dangerous than it is today when they only have Mbappe.