Newly built apartment (KfW-55) cannot be cooled, always at least 25 °

Can’t you cross-ventilate the bedroom with other rooms in the evening and at night?

We have a kfw55 house but have absolutely no problems.
Some windows and doors are open during the day, and if it’s 30 degrees outside, I have the same inside. I don’t mind, in that weather I’m outside anyway.
In the evening there’s a draft through the whole house, the heat goes out quickly, usually it gets a pleasant 25 to 26 degrees.
Only the bedroom with west-facing windows (however the sun only gets there late) we shade with roller shutters during the day. Then in the evening the window is opened, overnight the window stays open and the shutter is pulled down, only leaving about 20 cm open at the bottom. That way we can sleep really well, the bedroom is max 24 degrees in the evening, mostly only 21 to 22 degrees in the morning.
From my point of view, ventilation at night is the most important.

Your husband is worried about break-ins with the windows upstairs? Where do you live? Somewhere where it’s even bright at night and you need soundproof windows at night? That’s of course annoying but shouldn’t be the usual case with single-family houses.

By the way, we have a bungalow, so the bedroom windows are on the ground floor. That’s why the roller shutters are pulled down about 20 cm and the window is open. Burglars don’t want to get caught, they almost certainly won’t break into an occupied bedroom. That only happens in crime novels.

We live in the countryside. In a new development with about 20 houses at the end. If you want to sleep longer than 7 a.m. on Saturdays, you'd better close the windows. Children's noise, neighbors working, cutting tiles, paving, chopping wood, mowing the lawn, etc., etc.... And mowing the lawn and kids on Bobby Cars will also continue. Yes, and at that time it's already bright for a long time. And we don't have roller shutters but window shutters... you can close those and then a bit of air still comes through.... But he doesn't dare to leave them open on the ground floor either.... Because we actually sleep upstairs; if someone tried to get in there, we wouldn't notice it at all? Yes, maybe not in your bedroom but if you have the other side of the house open for cross ventilation?

Burglars do not want to get caught, they almost certainly do not break into the occupied bedroom.

They also break in less (not at all) in new housing developments because they know there is nothing to get there. (Exception: villas)