So far I only see Bayern Munich who are seriously active in improving their squad for next season and therefore they have completed deals with several players. However, other teams such as Leverkusen, Dortmund, Leipzig have not yet seen their movements in the transfer market this time and only a few rumors have emerged.
Is it possible that some of these teams are still monitoring the talents who are currently competing at Euro 2024? because every time there is a competition, it always produces shining players who will be competed for by various teams. On the other hand, I know that the depth of their current squad is no problem at all and I think if this season there are no additional new players then they are confident with the squad available.
Probably many teams are monitoring players in Euro 2024 as well. Euros have a really good impact on teams to make their transfer choices.

I think Leverkusen won't need to make big changes this summer. Because they seem likely to keep a serious part of their squad from the previous season. Tah might leave in case he wants to sign for Bayern Munich while they have some interest in him. Then Leverkusen would look for signing a centre-back. Even Wirtz is staying but for only 1 season for now.
Dortmund is closing in on signing Guirassy from Stuttgart. Thinking he has only a release clause like 17.5 million euros, it would be a great job.

They are interested in Ferdi Kadıoğlu from Fenerbahçe too who is a really good talent. Maatsen's loan spell is ending so they will need a LB transfer.