Is there something about the way lemmy works that is causing Sync to chew up so much data? I never saw this kind of usage on Reddit.
Not that far off from mine! Interestingly, my Sync used almost as much as Meet (which I use daily for video calls).
I suspect it's mainly multimedia data, like high-res images. Maybe Lemmy serves higher-res images compared to Reddit? I also recall seeing some discussion somewhere were Lemmy instance admins were turning off server-side image/thumbnail caching, so as a result you could be directly pulling the high-res images by simply scroll thru your feed? This is just a guess though.