The value is stored and synced on Jellyfin.
If other players do not handle it there’s not much I can.
All other media center have proper integration (Plex offer the store resume settings per library) Emby have proper audiobook section. Jellyfin choice may fit it’s own needs as it can play everything (but what happens when you play an album with both images and music to an audio only player) but it’s clearly not suitable for other apps to consume properly.
I only integrate things that works 100% or don’t integrate as anything below triggers too much support for what I can handle.