It looks like AAD sync is up and running - it's working with one of my tenants. However, on a second tenant, Edge is telling me that my administration has disabled sync. This is a surprise as I'm the administrator. I can't seem to find a setting for this in AAD - is there one? Or is this just a rollout issue? Thanks!
So it appears that the issue is that it requires AD Premium, in particular - Enterprise State Roaming. I had two tenants, one with, one without. One worked, one didn't. I lit up AD Premium on the one that didn't and after a little while, I was able to get it going.