Will I be able to play Opendev LUCY if pre-purchase this game through Epic Game Store? In the opendev LUCY page, only steam is mentioned. So I need clarification. Thanks

Not from what i understand. You can, however, watch a sponsored streamer playing humankind live on twitch for three hours in order to unlock access to the Liucy opendev without having to pre purchase on steam(details in the Twitch drop thread)