In the latest Edge insider Version 81.0.375.0 (Official build) canary (64-bit)
Favorite sync is working (Haven't tested whether it still generates duplicates or not)
Favorite sync has become a Controlled feature roll-out (not available to everyone in all countries) (tested with different VPN servers)
Favorites set to Icon-only are reverted back to normal state when more than 2 devices sync with the same Microsoft account, the browser can't tell whether a favorite entry is set to Icon-only or not so can't sync that state either.
Collection syncing is working Correctly.
Passwords and Address sync are working Correctly.
Settings sync doesn't cover all of the Edge settings, only a few of them.