> The "look and feel" of the program usually gives it away more or less immediately.

If you are talking about the base controls, then maybe. But there are .Net cross-platform frameworks such as Avalonia that can get you a modern loooking UI with theming.

https://github.com/irihitech/Semi.Avalonia

https://github.com/AvaloniaUI/Citrus.Avalonia

etc.