I have a smattering of books on Kindle, mostly fiction/novels. But the vast majority of my book conllection consists of non-fiction/textbooks and I recently switched to Booklore on my NAS. I have over 900 textbooks and can access them anywhere via a WireGuard VPN. It's so slick!
Booklore seems great, but I'll admit there may be even better options. However this is the future of books for me. I'd like to start replacing more and more of my physical books with pdf/epub copies. It's been hard because there is nothing I love more than sitting down with a physical book. But this is definitely far more convenient.
I now want to start building up a research paper library in the same system.
There was some whole blowup with Booklore over it being vibecoded by a single maintainer recently. I think the project has changed ownership since then, but be cautious.
I use Calibre + Calibre Web. Definitely a bit old and clunky, but reliable.