Something has changed in the last few months. There was a discussion on this last year in the Kobo forum. At that time, annotations would sync between the e-ink device, the iOS and Android apps and the desktop. There were some timing issues based around when the different apps did their syncs, but it worked. Trying just now, there is no bookmark sync be the apps. And there doesn't seem to be bookmark syncing between the e-ink devices.
The earlier discussion is in
https://www.mobileread.com/forums/sho...d.php?t=256685 and
https://www.mobileread.com/forums/sho...62#post3056862.