The "portable" one is not a hard requirement. It's a whimsical self-imposed constraint, which makes as much sense as complaining that you can't stand on your right foot on Tuesdays. All installer toolkits released in over two decades support deploying arbitrary components. Is this not a solved problem?
WinUI3 supports dark mode/theming out of the box along with fully customizable styling. It's as free as it gets. It's also Microsoft's official GUI framework for Windows. But the blogger rejects it because... Because what?