You won't be able to read library books on it after it resets (which it will eventually) unless you jail break it. My son jail break'd his kindle so I guess its not too hard and you can read library books that way.
No Kindle Unlimited, though, and library apps will probably drop support for the older stuff in time.
Jailbreak on very old Kindles is reasonably straightforward and the fact that Amazon hasn't even put out point releases to stop it (as the do with newer models) is a strong hint that they've just given up on maintaining them. I still have a K3 (Kindle Keyboard) that not only is jailbroken: it runs Tailscale.
Unprotected books, no problem. Anna's Archive + Calibre will keep working just fine.
I got an android based epaper device and installed Libby on it. Overall it is a much better experience than doing the library to Kindle dance. I can just browse my local library's ebook collection on device and immediately open them in one tap.
Battery life standby time isn't nearly as good, but being able to also read Notion pages, review full PDFs, and other benefits from having an actual tablet, make the battery life sacrifice worth it.