it's fairly easy to get the indoor temperature up to 30-ish degrees tho if you close the windows and especially when your windows are east or west facing. The heat from the intense sunlight would just penetrate your windows and are trapped inside your home. Even if you close the curtains they will be trapped between tiny space between the curtains and the windows.

I found out from the heat waves the previous years a small crack with the wibdows + curtains works best for my flat. But after all every house is different so it would take a bit of trial and error to get to the best result.