How to sync epub / pdf read state accross devices?

Starting to pull my hair. Is there any way to sync epub / pdf read state across devices?

LibreraReader has an export / import function which includes Bookmarks as per Librera

But then again export to e.g. Nextcloud folder results in error, meaning the exported file ends up on device without sync.

Backing up to device, moving file to Nextcloud and then importing on the second device is feasible but not convenient.

It would be great if bookmarks could be saved to the files metadata. That would resolve the manual overhead of the export / import dance, since then the files could just be synced via Nextcloud, Syncthing, other_alternative.

Is this somehow possible with an app from f-droid? If not, what other app can do this?