Thanks, that was helpful:
(codeblocks:4452): Gtk-WARNING **: Unable to locate theme engine in module_path: "oxygen-gtk",
Exception: An exception has been raised!
The application encountered an error at configmanager.cpp, on line 239.
The error message is:
TinyXML error: Error document empty.
In file: /home/<>/.codeblocks/default.conf
At row 0, column: 0.
So I deleted default.conf and it launched. Now, is there a way to force the package manager to update CB to v12? As I mentioned in the previous post, simply adding a software source does nothing