저기: Devil's Kiss
Is it a Gog error?
Good spot! It used to be free with every purchase of Lair of the Clockwork God. No idea when this became permanently free without purchase though.
On another note, Legend of Nayuta purchases will come with free Official Digital Soundtrack from the 19th till 26th of September 2023. After that, the digital soundtrack will no longer be available for sale on Gog.