I run Koreader on a Kobo Libra 2. I just connect to my OPDS catalogue on my Calibre-Web instance. It’s not exactly a sync setup; it just gives me access to my library whenever I need to download something, and that covers my needs. There are several other sync options; check out Koreader’s features here: https://github.com/koreader/koreader/wiki
If you like it and decide you want to it, go through the list of supported devices and see what sort of sync capabilities are available for them (support for Kobo devices seems to be the best/have the most options).