PSG are the kings of ligue 1 and no single club can compete with them. They are always consistent in every match and always win it. Mbappe, Messi and Neymar are the most dangerous trio so far for any club in Ligue 1, it's clear that PSG will lock in the Ligue 1 title this season. About fighting Bayern Munich in the UCL competition it seems that it is quite difficult, these two teams are the same as the top standings and indeed from statistics Bayern Munich always excels in UCL matches, so I think Bayern Munich will win this match again when they meet PSG later.
Staying with the tag of King of Ligue 1 has never been ideal because they want to be King in Europe as well with this squad and quality because now things are to change, and they must need to achieve this which is possible in this season because now they are impressive in all departments even in last few matches they have issues, but they are still able to settle these things quickly.
Mbappé saga is surely right now at the top, but they also need to have good results for having better future and maintain their this system now after two months they are going to face Bayern Munich which is also having same tag in Germany even their record in Europe is also amazing which will help them for having better results, but now we will have good contest between these two teams and first test after world cup for the Mbappé and Messi.
Even though PSG is a strong team in Ligue 1, PSG doesn't always win and can still be beaten, at least PSG isn't always easy to win. Because after all, so far this season PSG has also got two draws in Ligue 1, these results certainly prove that even though they are the strongest team, they are not always easy for PSG to gain full points.
So yes, a king or not, in reality they won't always win in every match.
What's more, PSG in Ligue 1 haven't won enough titles, and if PSG wants to be like a more perfect king then PSG must be able to win more Ligue 1 titles and in a continuous way like Bayern Munich in the Bundesliga.
But regarding the match in the Champions League against Bayern Munich, basically PSG still has a chance to win, because at this moment the PSG players are in their best performance and chemistry. So yes, I personally am pretty sure that PSG can still beat Bayern Munich.