How does air circulation work in japanese homes (not traditional)?

Here in France we have air inlets above windows and when i look at japanese homes interiors i don't see anything like these air inlets or holes that could indicate air is circulating and renewing.

The thing that "drives me crazy" is that due to these air inlets, thermal insulation is diminished. You pay for a good insulation and yet you have to install these air inlets to comply with legislation, air inlets letting hot/cold air coming along the rooms.

I'm not trying to say that japanese homes are better or blablabla but i can't find some relevant stuff on internet about this and i'd like to understand the way it works in Japan.

One other thing i saw in a video was a japanese shower room (which is very japanese… not common at all here in France). There is a window inside it and it seems that the room is also dried by the heating (not at the same time) . BUT here where i live we have some serratia marcescens issues. According to what i found, this pink bacterium appears because of residual shampoo/soap grease and mineral and because the room is humid and hot (in the shower room). I have a window and a heating and a controlled mechanical ventilation in the room… the bacterium appeared when i started to use the heating (a towel dryer) it dried the room faster than the window but the bacterium appeared… there must be this kind of issue in these japanese showers …? (i'm not asking to resolve my bacterium issue)