Is it normal to have this hole above the bathroom doors?
No, this is not normal, they left the tiles too short, and the door flashing does not cover the gap.
One solution is to change the side covers and put them a centimeter wider, and the top cover the same way, that is, 1 cm wider, so that it covers it well.
The reference to ventilation is a cop-out. It is a mistake of execution, which should not be allowed, and unfortunately, it was not filled with polyurethane foam or putty, which is also very common...