CBR and CBZ files are marked as read when connecting Panels via OPDS to a Kavita backend. However, the same doesn’t happen for PDFs or EPUBs on a Calibre-Web backend.
This would be a useful feature to offer on Calibre-Web, acknowledging that it might not be possible given Calibre-Web’s OPDS implementation. Apparently sync is possible on Calibre-Web using other platforms (e.g. Kobo, KOReader), although I haven’t personally validated that it works.
OPDS does not support reading progress sync. We sync with Kavita and Komga because we’ve implemented a connector to their API (outside OPDS).
Since OPDS announced they will support reading progress sync in future versions, we will add support for it and, hopefully, Calibre will also adopt that version of the protocol.
For now, we’ve decided not to make ad-hoc implementations because they require separate maintenance.
Hopefully, soon the protocol will support this.
I hope that makes sense.