Engineering: Mystery of the Ancient Clock

Prices in official storesiOfficial stores sell the key on behalf of the publisher (Steam, GOG, Humble…). Keyshops are third-party key resellers (Kinguin, Eneba, Instant Gaming…): they cost less but aren't the publisher's store, and support and refunds go through them. Check the key's platform and region and prefer sellers with many reviews. On Linux what matters is that it's a Steam key: the game starts with Proton just like one bought on Steam.