Basically, the big teams will certainly put a lot of focus on the Champions League, so it's no wonder that the big clubs can play better in the Champions League. Although sometimes, they are not in a good position in the local league, but in the Champions League they will make every effort to get good results too. So yes, of course Manchester City will also not be weak next season, with a successful treble winner obtained last season it will certainly make Manchester City even more ambitious next season. But even so, I personally do not fully believe Manchester City will easily get the trophy, because other teams will also be ambitious to get rid of Manchester City.
It is true that all clubs will try their best in the Champions League because apart from being the number one club in Europe, clubs that qualify for the Champions League will get a big bonus, will also get a share of TV broadcasting rights and so on. As far as I remember, the amount of bonuses given depends on how far the clubs have progressed. So it's only natural that they will maximize all their potential to go further, lucky if they win it like Man City last season.
I have some doubts about Man City after looking at their transfer market, a lot of key players have been let go like Mahrez recently joining the Saudi Pro League. For sure they need some time to get into top form after so many changes in their main squad.
It will be extremely difficult for the squad, regardless of how great it is, to regain its past prominence if some of its players leave. Manchester City is renowned for being strong and cunning as one of the best teams to win three trophies in a single season. However, I don't think they'll do as well as they did this season next season because the team's greatest players are going, and even if they replace them with another player, the position won't be as strong as it was before.
The champions league will be one of the most anticipated events of the upcoming season because it will be a huge challenge. Based on the preseason performances of arsenal and Bayern Munich, I believe that these teams are fully prepared to compete in the champions league and that the other teams should do the same.