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

It looks like in the slums without wanting to offend them.

I don’t care what neighbors think about it. I can only say that, as far as indoor temperatures are concerned, I didn’t do much wrong. A statement like the comparison with slums just reveals how arrogant and out of touch people have become towards others (things). In case it’s not clear: for the previous photo, I arranged the cloths, gladly called "rags" by Katja, so that you can see all the arrangements. I think I didn’t do much wrong if I can show everything in one photo. Slum residents might not be as dumb as the rags they hang up.

Thank you for the answers. I am the landlord and could quite imagine installing blinds - at least in the living room. What type of blinds would be most effective?

I don't care what neighbors think about it. ... Such a statement [...] just lets you guess how arrogant and out of touch people have become towards others (things).

Funny. As I said, I didn't want to offend anyone.

I am the landlord and could quite imagine installing blinds inside - at least in the living room. What kind of blinds would be most effective then?

That helps little to nothing. Once the heat is through the glass, nothing can stop it anymore.

I also strongly doubt that the installed heat pump has a cooling function.
The most electricity-intensive would then be the LW, the brine only costs a little pump electricity.
And once the heat is in the house, you can't get it out even with the great cloths, at best stopping further temperature rise.

I read, since spring? The underfloor heating was still running then.
Has the tenant ever interviewed the other residents of the house? Especially those on the same side and directly above.

That brings little to nothing. Once the heat is through the window, nothing can stop it anymore.

You don't know my rag curtain construction. What you say is not true. It makes a difference whether you still hang curtains/rags/other things inside in front of the window or not. Maybe not after 3 weeks of 30°, but every day you can avoid the heat inside is pleasant. Plants in the house also help to make the indoor climate feel less warm. All together, that's more than nothing.