Strong discoloration of oak parquet due to sunlight exposure

What you describe is the normal development of oak. Every wood undergoes a color change. This is caused by exposure to daylight. Therefore, it is clear that in fully covered areas, where no light exposure occurs, the floor remains light. There is the option of sanding. If not, it is important to know that the light spot will catch up with the color development and thus gradually match more and more. However, this requires patience.