PSG and Barcelona in my opinion will be the favorites next season ahead of Real Madrid, Manchester City and Bayern. I don't anticipate them to be any weaker for a good reason. Both of them are not losing a lot of players due to transfers as far as I know as of now and both teams have the majority of players being at the perfect age and all of them are humble and willing to improve.
Next season UEFA will be a different kinda ball game for the team you mentioned, fighting for the UEFA trophy. I don't think PSG and Barcelona will be more favored in lifting the Champions League trophy next season, as other teams are making new signings to their team, to boost their formation.
PSG and Barcelona had the best season last season, next season we don't know if it will be the same treble and double trophy will be won by them next season. Last season, Manchester City and Real Madrid won no trophies; who could have thought of such? Next season, such a surprise could happen to PSG or Barcelona to win a single trophy, and it may not be the Champions League
They will all have to cope with uncertainties while PSG and Barcelona, if the teams remain like they are for the most part, can keep growing from where they are. That can make a huge difference during a season. Uncertainties like injuries are a risk for every team and can change a lot for the worse out of a sudden, but if for example Barcelona is not running into serious physical problems during the next season, so many positions will be taken by outstanding players that have already played so well in the past season. There are no bad signs so far, no reason why Raphinha and Yamal would not perform their best for Barcelona or why PSG would not play as well anymore because they now won the CL. I think both teams will once again be able to deliver high quality performances all season long.