The problem is that the windows might not be suitable for window units. For instance in the Netherlands our windows typically tilt or turn (like a door) open, they don’t slide up. The walls and ceilings are usually solid brick or concrete, so you can’t hide ducts in there for central AC. That leaves a split unit in one room or a portable unit.
Blocking the light made a huge difference in my house. I have are 3 small skylights on the south side that now have sun shades on the outside. They still let in some light, but it’s at least 5c cooler on the top floor.