There are cosmetics only, and they're earned through XP.
Doom Eternal will not have microtransactions, Creative Director Hugo Martin has confirmed.
Responding to a fan in Facebook comment that’s been screencapped and shared online, Martin asserted that Doom Eternal has “no store”.
“Nothing [you] can unlock in Eternal with XP has anything to do with player abilities or content that would impact your game in [any way],” he wrote. “The only thing you can unlock with XP is [cosmetics]. Those cosmetics have no impact on how [you] play, they just look cool.
“Eternal is a $60 game, not a free-to-play game or a mobile game – we are giving [you] a complete experience with no store just like you’d expect. Unlocking skins with XP is a part of the experience if you care about that stuff, or [you] can completely ignore it.”