I have 3 different libraries, one for comics, one for TTRPG books, and my main one for actual eBooks. My main library is over 4GB with over 1,000 books.
No, I haven’t read all of them, but I am working on it. They have been collected over the last 15 years from Sony eReader store, Kobo books, Amazon Kindle, B&N, Archive.org and other Public Domain books hosts, Humble Bundle, Story Bundle, and various other places.
Largest categories are Sci-Fi, Fantasy, and Mystery.
I wish there was a way to link to an Android app.
I think at one point I had 14,000 books when I was a teenager (all pirated.) I’ve since deleted most of that and have sub 200. It’s all in one library now but I used to have one for Textbooks/Nonfiction, Fiction and one for Cooking. I have been trying to do things more ethically this time around but I really don’t like DRM because you don’t really own the eBooks you purchase.