"To select what kinds of browsing data Opera syncs between devices:
From the main menu, select Settings.
Click Browser on the sidebar.
Under Synchronization, click the Advanced Configuration button.
Tick or untick the checkboxes next to the data types you wish to sync."
is not possible. The helps says also:
"Once you sign in, the browser pushes all of your device's browsing data into your Opera account. The same will happen when you sign in on a different computer, on your phone, or on your tablet."
This does not happen. The page always tells me I have no saved data, I should log in first. Hm. I AM logged in. What can I do?