Author here. Here are top advantages from the top of my head

* pywebview hides its browser nature. Right click, text select, shortcut keys, swipe gestures etc are disabled by default.

* window manipulation functionality. Move, resize, minimize, maximize etc

* native file dialog support. These are more capable than browser's own file dialogs.

* native application menu

* with the new version you can get a full file path on file drag and drop. This is not possible in browser.

* two way Javascript-Python bridge. You can invoke Javascript from Python and Python from Javascript

* If Javascript is not your cup of tea, you can do quite a bit in pure Python.