The full version will be available to download for free when it is complete. A Steam release (or any paid release at all) would not be viable because of the music this game uses, and I don't have any plans to ever sell it.
What do you mean by "the music this game uses"? If you don't have the rights to the music you shouldn't be using it regardless of what platform you're publishing on! If it's something like the music rights are only valid for non-commercial works, you can still publish it on Steam as a free game!
Steam supports and hosts many free games, and publishing it on steam would be awesome. This game is really fun on the steam deck!