I didn't expect this one to be the most fun and most efficiently programmed version of Solitaire on itch.io, that'll teach me not to judge a book by its cover. And your art is also really good.
I'm a bit confused by the winning condition, since it seems to require that all cards are face-up, including those in the side deck, and specifically in only four piles, regardless of whether they start on a K.
Not that I'm complaining. I found it a slightly odd choice, but it certainly beats having to sort all cards manually when the game is already won.
So yeah, excellent work!