OT: another site where you have until January 31, 2022 to download your purchases is Pottermore. They gave a lot more notice--the shutdown was announced in 2019.

I somehow missed that, but they sent an email at the start of this year reminding users of it. Go to https://bookshelf.pottermore.com/ and enter your email. They will mail you a link to your bookshelf.

Follow that link and you'll find all your books with download links to download DRM-free ePubs.