Agreed, you will do well with either QT or Swing. Or just a web application. However let's say you want to develop a vfs using Dokany, then a windows image is very useful.
Nothing is stopping QT or Swing from having a bug that only happens on Windows (or any other operating system).
With web apps if you want a more native look/feel/need more native integarations and decide to use something like Electron you can still have platform specific issues/bugs.