It no longer does for the first few generations of Kindles. My Kindle Keyboard (16 years old, but it still works and I still use it almost daily) is essentially a useless paperweight now, as far as Amazon is concerned. De-registering it will brick it and they shut down the "send file to e-mail" service, too. Can no longer buy and download books off Amazon either (they shut that down in 2024, afaik).

If not for Calibre, I would have absolutely no option of ever getting new books on it.

So it still works as a generic ereader via Calibre? That seems like a pretty fine outcome. I don't think Amazon (or any company) should be on the hook supporting a device for 16 years. I can't think of any company which does. Dropping support for old devices frees up eng resources. If you've ever worked in a shop needing to support legacy devices, it becomes a huge burden to keep up support (especially as the supporting software/hardware starts to degrade, like 3P updates) for what becomes an increasingly small number of users. Of course, if the number of users remains significant, support should be maintained.

I've decided with all my commercial e-readers that the USB+calibre is my only option as I do not wish to share my reading habits with the zillionaire overlord.

There might be new and fancy UI or something, but I spend 99% of the time only flipping pages so the outdated UX is nothing compared to the privacy I get.

Ancient Basic Kindle works still nicely and so does 1st gen Paperwhite + the few Kobo's we have in the family.