I even tried using it to synchronize my collection from my desktop to my phone
I use Calibre-web on a home server for this. It’s a web interface for a Calibre library that has an option to send a book to Kindle (via the Kindle email address), and it also has an OPDS server that can be used with good ebook reader apps like Moon+ Reader.
I actually forgot what I tried to use, but IIRC it’s a Calibre add-on that allows me to mark the books I’d sync to my phone. I think it kinda worked, but for my purposes, it’s way too much work. Well, way too much work as opposed to just copying the books I want on my phone to a special folder which is then seamlessly synched via Synchthing when I connect to my home wifi.
I use Calibre-web on a home server for this. It’s a web interface for a Calibre library that has an option to send a book to Kindle (via the Kindle email address), and it also has an OPDS server that can be used with good ebook reader apps like Moon+ Reader.
I actually forgot what I tried to use, but IIRC it’s a Calibre add-on that allows me to mark the books I’d sync to my phone. I think it kinda worked, but for my purposes, it’s way too much work. Well, way too much work as opposed to just copying the books I want on my phone to a special folder which is then seamlessly synched via Synchthing when I connect to my home wifi.