Moon+ Reader has a built in cloud sync function and so does KoReader although I can't say more about KoReader as I only keep that installed on my old kobo.

Here's the link I followed to set up cloud sync for reading positions/notes/bookmarks:

https://raymondlamsk.blogspot.com/2018/03/moon-reader-how-to...

Calibre is a very useful piece of software regardless of what ereader you end up with, and there's this feature request about syncing back to calibre too but I haven't personally explored it. https://github.com/koreader/koreader/issues/3814

One annoying thing I sometimes run into is that if you keep wifi off, you'll have to remember to turn it to sync. But that's understandable.