It’s through Overdrive, a service that lends books to library patrons. Overdrive’s current interface for mobile devices and browsers is known as Libby. At one point in time, both Kobo and Overdrive was owned by the same company.

Note, libraries only offer a small selection - the selection mine offers is a lot different from the library up the street from me. It’s all curated from organization to organization.

Edit: Overdrive also operates Kanopy, a library video streaming app; as well as Sora, an K-12 reading app.