In France, shutters aren't like most American ones, here we mostly use either plain wood with no gap for light (old houses) or for most of the recent houses, we use rolling shutters that let 0% of light (and therefore, 0% of radiative energy from the sun) get to the window and will make the room entirely black. Also, most modern rolling shutters are white by default so they are pretty reflective.

In the current situation, it's the air temperature that fuck us by not getting down at night and so our (concrete) buildings accumulate the heat even at night.