Not looking for a tutorial. Figured it all out after dicking with it for an hour. Looking for opera developers to improve the workflow.
If anyone cares just try doing a dry run of this process as a new user, presuming zero knowledge of the app, and see how much effort it takes.
For me half the problems stemmed from google authentication indicating I was logged in but then not syncing anything. Then the synced tabs page is just blank not indicating anything helpful, have to go to settings to find out anything's wrong. Then when I finally figure out you need an extra passcode on top of google authentication for some reason, and I enter my old one, opera no long recognizes it - passwords apparently expire, or get screwed up when you start selecting log-in with google. When I get on my pc to figure out what's going on with my account, it's showing my old device several times from each OS update. Then the page of synced tabs are simply not up to date for some reason for several minutes, and there seems to be no way to force a refresh on either end. Then when those finally populate I go to my new phone and have to load in each tab one by one. And there's another step to import speed dial sites. And when you select a synced tab to recreate, the behavior is inconsistent between creating a new tab (if I'm on speed dial) or replacing the current tab (if I'm on the last tab I just populated). Just a total mess.
Sorry if this seems overly negative. I love opera on mobile so I will be sticking with it, this just seems like an area that could be hugely improved.