I put my phone in airplane mode. I filtered to songs available offline. I hit Song Mix to start a mix. I rated a song (Mouthful of Diamonds) with 3 stars. I skipped tracks forward a couple times. I turned off airplane mode. In the main filter button, I reconnected to Navidrome, and I tapped on Sync. Once the Sync was complete, I searched for the same song. It had no rating. I checked in the Navidrome web UI. The song has no rating.
The feature request at Support offline rating as done for favorites described similar behavior of rating offline and having the ratings get lost, but that’s ostensibly before you implemented this feature.
In this test case, I didn’t listen to the song long enough for it to count as a play, but I’ll note that earlier today, when I similarly listened to several songs in offline mode, it did record the listens to Navidrome and consequently to Last.fm and Listenbrainz, so it seems specific to the ratings aspect.
