oh, no no ... I guess I described it wrong ...
backUp files = copies of files (and folders) from the specified path.
I don't use Sync at all ...
I'm doing exactly what @Gateau wrote in the original post:
transfer personal settings the first computer's Opera files onto a different Opera installation on a second computer.
And I just checked it out - I'm writing from a work PC (new installation of Windows), where I've now copied the 2 folders and 6 files from the Home PC.
In the case of the portble version, these files are of course not copied to the "... Roaming ...", but directly to the Opera folder in the "Profile / Data" subfolders.