I've been a happy paying subscriber to Kindle Unlimited for years. To me, it's like a library that you pay $10 a month to access. You can borrow up to 10 books at a time and keep them checked out for as long as you'd like. You can also listen to audiobooks and subscribe to three magazines.
Kindle Unlimited includes the Harry Potter series, The Handmaid's Tale, The Lord of the Rings series, The Essential Calvin and Hobbes, Locke & Key, and a couple of million more titles.
Right now Amazon is offering four months of Kindle Unlimited for free. The deal end June 23, 2021, 12:00 AM.