That fresh-profile test is the most useful clue here: if a completely fresh profile fails in exactly the same way, the problem is very unlikely to be your local Sync data, so rebuilding that folder again probably will not help.
The wrong-password error also tells us something — your sign-in itself is working, but Sync then is not completing. A couple of things worth checking next:
- Open opera://sync-internals and look for any error shown there, and whether it says Sync is running at all. That usually shows whether this is an account or server problem rather than a browser one.
- If you have another device where your passwords and bookmarks are still present, make sure they are backed up or exported first. Then, in your Opera account, reset your synced data and sign back in — that clears the server copy that the fresh profile is still failing to read.
- As a quick check, try signing into Sync in Opera (the standard build, not GX) with the same account. If it works there, the issue is specific to GX; if it fails there too, it is almost certainly on the account or server side, and Opera support would need to look at it.
The greyed-out passphrase option fits with that too — it only becomes usable once Sync has actually connected.