I want to empty my old Medion Akoya notebook because I want to sell it. How does it work?
You can either remove the hard drive and install an empty new one.
Or - I suspect you still have an HDD - you overwrite (technical term wipst) it, for example with a live Linux like DBAN. Then only minimal fragments of your data remain in so-called reserve areas.
But then there's no longer an operating system on the laptop and the buyer has to set it up again!