Maybe it's too early to draw conclusions? Bayern is also not in first place in the Bundesliga and even City is not in first place in the Premier League. All three clubs are very close to the top and remain the bookmakers' favorites, so it is too early to talk about serious problems.
By the way, as I said, Mbappe scored two goals yesterday, showing that he is in excellent shape and his decline in performance at the club level is temporary.
Indeed, it's still too early. PSG can still show their best to their fans later, right now also they gap only 2 points different with Monaco. So PSG can still race to win the title, and yes you're right PSG is still the favorite team so it's possible they can still secure the title. Mbappe yesterday became hero on French team with 2 goals, Mbappe performance in scoring is actually still great, although Mbappe performance with PSG this season is not that impressive but yes is temporary.