The PSG management tried hard to strengthen the squad and win the Champions League title. The best players in the world were added to the squad for huge sums of money by the PSG management. But their biggest mistake was that they did not hire an experienced coach. The squad had many star players. Star players are very difficult to handle. This is not possible without an experienced coach. I think this was the biggest mistake of PSG management.
But last season PSG management appointed an experienced coach like Luis Enrique. Now if the PSG management gives Luis Enrique full freedom and big funds then maybe Luis Enrique will be able to strengthen the PSG team.

They should focus to strengthen their team to win Ligue 1 instead of Champions League, there's no guarantee they will win Ligue 1 especially without Mbappe, I'm sure they will struggle and we will see a competition in Ligue 1. PSG to win Champions League is just a dream that impossible to achieve.
If PSG didn't win Ligue 1, we all know what the cause is.
You are right that there is no guarantee that PSG will win the Ligue 1 title. Without Mbappe, this team will undoubtedly be a bit weaker than last season. Mbappe was PSG's most important player and main striker. So the impact of Mbappe not being in the squad will certainly be seen to some extent.
But Luis Enrique is an experienced coach. At the same time, PSG have no shortage of money. Management does not skimp on spending money. Luis Enrique will have enough funds to add the players of his choice to the squad. Luis Enrique will certainly be able to find a worthy replacement for mbappe. So personally I don't think it will be difficult for PSG to win the Ligue 1 title.