Can we override only files in the Template folder or other files too?
If I want to override a controller (example)… do I have to duplicate it into my own plugin controller (as a controller) and work from there… or can I just do a template override ?
This is OO programming. Your Controller can extend/derive from the relating controller.
Of course, you could clone and extend the code, but this is IMHO bad practice.
class ConfigController extends \Kanboard\Controller\ConfigController {
// usual implementation
}
class MySpecialConfigController extends ConfigController {
// additional stuff goes here
}