I use BookFusion. It’s a paid service but syncs the library and progress across platforms. Integrated with Calibre too, which I saw you mentioned you use in a different comment. Works great for me, but good luck finding something that works for you.
Yeah this is all over. Here’s another one about Io9 publishing an AI article with tons of mistakes and no chance to even edit it. Not sure who thought it would be a good idea. AI can be very hit or miss on first go and needs editing before use at the very least.
BookFusion is cool. It also has a calibre plugin so you can upload directly to it if you use Calibre. No idea how they are privacy wise but the sync is perfect across multiple devices and systems. It is not open source but it does what you want and has paid levels. Here’s the link: https://www.bookfusion.com/
Oh,I think you’re right. They have their Calibre plug-in which is open source I think but I think in my head I conflated that with the whole app. My bad.