Dockerize a windows GUI application
I'd have to say that I don't think it's possible and if you understood windows containers you really wouldn't want to do it anyway. Last time I checked, a windows container weighs in at gigabytes++ and that's huge to run notepad.
You can run xwindows apps in a container, but windows is, basically, complete shite in a container.
If you want a sandbox then you should checkout VirtualBox or Hyper-V. You can script either with Hashicorp Vagrant.