Real Madrid, Man City, Bayern Munich or Liverpool, they are all strong candidates for UCL this season who have the opportunity to win the title and in my opinion Barcelona is the same with its current condition with Hansi Flick, they deserve to be included in the category of strong candidates accompanying the 4 teams.
And to answer your doubts, let's just leave it to Barcelona, especially Hansi Flick, whether he is able to bring Blaugrana further in this competition or not or other possibilities present a trophy, no one knows. For now, let's just enjoy their competition.
They are strong at the beginning of season but now they have some risk of playing play-off matches to go to knock out phase in Champions League. We will return to talk about them as strongest and best candidates for UCL title in this season, when they already are eligible for knock out phase. Their current positions are not too good but still better than PSG's position.
I believe they will go far in Champions League this season, all of them Real Madrid, Manchester City, Bayern Munich, Liverpool and Barcelona. The exception will be PSG, as they are at big risk now or if they can go to knock out phase, it's hard for them to go too far. Losing Mbappe affects PSG's attacking system but their squad have more problems in midfield and defense systems too.