Windows are legally required for safety purposes, not for sunlight
but unironically; it'd be much safer than the street
I imagine there are plenty of people out there that aren’t aware that windows are for safety and might find out in the worst way possible.
They are not used for egress in skyscrapers—no ladder goes that high. And commercial buildings have fantastic internal ventilation. (Skyscraper apartment windows often can’t be opened for ventilation anyway, and are not trivially shattered.)
Limits I know are 1/8 of the flat surface you can march on must be openable windows, 1 complete air change per hour (you have a 50m³ room, you must change at least 50m³ of air per hour. There are some tolerance for historic buildings down to 1/12 of the flat surface, below that the accommodation can't be used to live in.
While for offices there is only an natural illumination requirement, and a ventilation NOT necessarily bound to openable windows. I do not know for the rest of the EU.