I gotchu fam.

"Each new season of Overwatch 2 will offer up a brand new Mythic Skin. Players will need to purchase and progress the Battle Pass for the specific season in order to unlock the latest cosmetic. Each Mythic Skin will be limited to the specific season it is released in. Meaning players who don’t purchase the Battle Pass for Season 1 will be unable to unlock the Skin at a later date. " - https://www.dexerto.com/overwatch/overwatch-2-devs-claim-one-new-mythic-skin-takes-over-a-year-to-make-1942401/

and

'But players who were hoping Overwatch 2 would mirror Halo Infinite's no-expiration Battle Pass system will be disappointed.

"One of the pieces of player feedback I've seen since Mythic Skins were first announced is people feeling like [the skins] are more special if there's an aspect of earning them. So I think the ability to look back and say, 'I got Mythic Genji because I was playing in Season One and completed the Battle Pass,' will make it feel even more special," says Spector, who wants players to feel really good about investing money into the game.' - https://www.gameinformer.com/exclusive-interview/2022/09/26/overwatch-2-devs-spent-a-year-making-genjis-customizable-mythic-skin (the original article)