Healthy indoor climate at a minimum of 24° C?

Maybe one should mention where they live, because here it wouldn't be 20 degrees anymore in your house either. Many greetings from the extremely hot southwest!!!

I have added it I believe we are among the hottest regions in Germany. But fortunately somewhat in the countryside - in the cities it is still a bit warmer due to the heated facades, streets, etc.

We have also had high temperatures for weeks and now beyond 30 degrees. Kitzingen is certainly another 5/6 degrees higher.

Then his measuring device is definitely broken.

Facade and roof shading by trees and solar also help. But the values are very low.

I don't think it would be physically possible to have a temperature difference of about 15 degrees inside and outside if it is hot for such a long period of time.

We also have 10 to 15 coolers without air conditioning.
At night it cools down and by manual ventilation it cools down for us quite exactly the 2-3 degrees that it heats up during the day.
It will just not work tonight because the lowest temperature does not fall below the indoor temperature.

[Shading and insulation keep the heat outside, the open windows let the cool night temperatures in]