To the best of my knowledge, there has never been a dark mode in iTunes for Windows.
I do wonder if the people who wrote your first link have mi-read this article your second link is about dark mode for Windows, not for iTunes.More to the point, the suggestion they outline is the setting for dark mode in Windows, not iTunes If the people who wrote that also wrote instructions for getting to the moon and back, I would not be confident of ever seeing planet earth again and I certainly wouldn't be travelling with them.
Not only that, but in an article specifically about dark mode in iTunes for Windows, it wanders off topic and talks about dark mode on a Mac, as well as about other features of iTunes that have nothing to do with dark mode. To the best of my knowledge, iTunes does not have a dark mode.
