With my ad-free paper white, there’s a magnet in the case that lines up with a sensor in the kindle.
You open the cover, and it’s right where you left off.
With the ad supported version, you’d open the cover, and have to push the button to dismiss the ad.
IIRC, that behavior still persists even if the ads expire.
This is how the case works.
With the ad supported kindle, there would be another screen showing the ad before you could use it.
Not a huge deal, but it does get a little annoying
It basically prevents you from being able to use the feature of the case
The ads were a lot less noticeable on the older kindles with the keyboard