ᐅ Severe discoloration of oak flooring caused by sunlight exposure

What you describe is the natural aging process of oak. All wood undergoes a color change caused by exposure to daylight. Therefore, it is clear that fully covered areas, where no light reaches, will remain lighter. There is the option of sanding. If that is not done, it is important to understand that the lighter area will gradually catch up in color and become more uniform over time. However, this requires patience.