So, I just set mine up with a tempmail (firefox addin) address, entered default info in airplane mode and then revoked network permission, it now works fine to control media playback (my fave feature). The tempmail only got a welcome to garmin email, no verification required. Steps update in the app offline fine. Garmin's sleep monitoring is for shit anyway (although more current models are apparently better, if not great, my VA3 is ~ 5 years old, still gets 3 days battery life tho). I'll get back to you with activities sometime, I do those via computer anyway. All in all, not that bad so far. It wants phone permissions etc, but that just lets you answer or decline on the watch, by which time I've picked it up. SMS allows a few canned responses, it's been useful on the occasional ride, but I'd prefer that to be me time. Anyway I declined those, we shall see.
Oh, installed from aurora fine without any google services.