Similar problem syncing Opera desktop with Opera Android like in the linked thread.
The odd thing is that it actually syncs some stuff like bookmarks and passwords, but not Speed Dials or Pinboards or Flow. Speed Dials arnen't even listed in the Bookmarks page.
Going to https://www.sync.opera.com/ only shows 1 device.
Trying to sync from the mobile app with Add Device only works partially (as already said) and seems a bit off. For example at the end of the procedure sync seems to be active in Opera desktop, but in the end it always fails.
Flow is different because I can sync it with the QR code method from the desktop app. And then the mobile app prompts me to "follow the instructions on the other device"...
... and the "other device" (on Windows) just hang up suspended in this screen...
... and of course there's no way I can use or isert the confirm code anywhere.
After some time (I don't really know at which point or after which action) after "thinking" for a while an error screen comes out in the Android app and I get kicked out of Sync status on Windows
Really odd stuff