It's up to the publisher whether content bought from the Apple store has DRM, not the store itself. Many books have it, but publishers like TOR and any books from Brandon Sanderson don't. There's sometimes a line at the bottom of the description that'll note it. For example, on Redshirts (https://books.apple.com/us/book/redshirts/id501758516)

> At the Publisher's request, this title is being sold without Digital Rights Management Software (DRM) applied.