Project Gutenberg https://www.gutenberg.org/ over 60,000 free Out-of-copyright (older) books that can be read online or downloaded as epub for Kindle or other ereaders.
National Emergency Library https://archive.org/details/nationalemergencylibrary?tab=collection">https://archive.org/details/nationalemergencylibrary?tab=collection has over 1,428,428 free, mostly non-fiction scholarly books and textbooks for students researchers and ordinary people. You can borrow up to ten books for 14 days with renewal available. Waitlists have been suspended so many people can borrow the same book without waiting for someone to return it.
For light reading, Amazon's Kindle Unlimited lets you "borrow" up to 10 ebooks at a time, for an unlimited period, for $9.99 per month. Their collection has improved since they first started and includes non-fiction and classics as well as new authors and some early works of now well-known authors. It is a good deal if you go through several books every month.
Google Books https://www.books.google.com has a similar subscription service, but I haven't used it myself.
Many public libraries still have ebooks,periodicals, and sometimes music or video available for download for their members through their website.