Two serious clubs, they just need to get their transfers right, and Real Madrid has already made a move. Trent is a big signing, but I think they still need one more solid defender personally, i believe Saliba would be a great addition to the team. As for Barcelona, if they keep the same squad, like you said, they could reach the final again. If Yamal keeps performing at the same level as he has so far, that’ll be a huge success.
We can only make predictions but the results can change, for Real Madrid themselves it will probably be much better than last season because they are so serious about overhauling the team by bringing in a number of new players and vice versa with Man City although at the moment it is not clear which players they will bring in.
Barcelona will continue to rely on a number of existing players and in my opinion for next season they will not be able to go further to the semifinals because a number of other teams will also evaluate the players they have so the competition will be much tighter, especially for Barcelona itself.
All teams that qualify for next season Champions League will definitely try to build better squad depth to become title contenders. Real Madrid and Manchester City really need to overhaul their squad depth so they don't struggle to finish in the top eight of the standings again, and the same goes for a team like Bayern Munich. It feels strange to see them fighting through playoff rounds just to reach the round of 16. Hansi Flick will likely also recruit new players to increase Barcelona chances of winning a trophy next season.