Microsoft is shutting down its ebook store, and deleting all its customers' libraries:
https://boingboing.net/2019/04/02/burning-libraries.html
The only reason they can do this is DRM, which means you never really own anything you've paid for.
Physical books are the most obvious alternative, but there are also DRM-free ebook shops. @libreture has a good selection here:
https://www.libreture.com/bookshops
You can find more book-related alternatives here:
https://switching.social/ethical-alternatives-to-amazon-and-goodreads
(via @yogthos )