For anyone else who is trying to figure out a way to mass import bookmarks from older versions of Opera, I found the Bookmarks Manager (https://addons.opera.com/en/extensions/details/bookmarks-manager/?display=en) extension to be extremely helpful. The extension has the ability to load a file with all of your saved bookmarks from other browsers, including older versions of Opera, and then mass import them.

This was extremely handy for someone like myself who has a ton of bookmarks