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.
To be really strong in the Champions League, of course every team must have players with extraordinary talents and that is not only for the main players, but also for some of the players on the bench because when a main player gets injured the team does not immediately experience a decrease in strength in the middle of the season. Barcelona's squad was quite good last season, but for next season Barcelona also still have to improve certain lines to be better than last season. Because when you get to the final the team must also try to win because the defeat that is more painful is losing in the final.
That is why many teams that failed to sign in potential players to change some of their weak players last season failed to get to final stage in this UEFA champion league final, because they make used of some players that made the team to lose this year trophy.
Team like Barcelona, Arsenal, inter Milan and PSG really displayed from the beginning of this UEFA champion league before PSG and inter Milan met for final for PSG to beat inter Milan to lift the trophy to break record through the help of the talented players they signed in the team. I believe many teams will release their old players who didn't perform well, so that their coach can bring in some new players that will make the team performance to improve next season.