GOG: https://www.gog.com/en/game/horizon_zero_dawn_digital_comic
Claimable without owning game. Add to cart, check out and select 'GIFT THIS ORDER' and gift to yourself. You will receive a code that expires on Dec 31, 2199. Note: you can't activate the code until you actually have the game.
Steam: https://store.steampowered.com/app/2107510/Horizon_Zero_Dawn_Vol_1_The_Sunhawk_Digital_Comic/
Game needed to claim.
Free until August 9 on both platforms.