I’ve currently got progress syncing through Calibre-Web-Automated, but I’d also tried it via KoInsights which I’m using for syncing reading stats. I’m in the process of migrating to my library to BookLore which also has a sync server.

I’ve been synching progress and stats between a pair of devices! It’s been great since it runs well on my haul broken kindle & my android.

There is some(maybe a bit more than some) setup time to get used to the layers of menus, but it’s a pretty robust app.