Bathroom ventilation system with electric fan
I can’t answer for the requirements in your country, but in the mainland United Kingdom, it is now a requirement to have a fixed mains powered ventilation fan in bathrooms and shower rooms regardless where these are in the building. This applies to new builds and in some cases, where renovation takes place.

The whole reason for having a fan is to reduce the humidity in the bathroom or shower room in order to reduce condensation.

The relevant UK regulations are outlined in the ‘Building Regulations Document F’

I presume there are similar regulations in your country.

I hope this helps.