We’re hoping that Lemmy will add a way to mark posts as read in batches - this would mean that we could locally store ~50 posts as being read at a time, then notify Lemmy of those changes with a single request. This would be the ideal solution for us, and we’re working with the Lemmy devs to make this happen.

Storing read posts entirely locally would certainly be possible, but doing it well would take up a significant amount of our development time. We are currently prioritising other highly-requested changes (supporting Lemmy v0.19.0, image uploading, and a better search tab to name a few) in the next few updates whilst we work things out with Lemmy :)