https://wccftech.com/doom-eternal-wont-feature-any-mtx-dev-were-not-a-mobile-game/

DOOM Eternal won't feature any kind of microtransactions. The confirmation came straight from id Software Creative Director Hugo Martin, who replied to a fan on Facebook.

No store. Nothing you can unlock in DOOM Eternal with XP has anything to do with player abilities or content that would impact your game in any way. The only thing you can unlock with XP is cosmetics. These cosmetics have no impact on how you play, they just look cool. DOOM 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 and it will have no impact on your experience at all and it's all free.