If you are worried about the possible presence of microtransactions in Doom Eternal, then you can calmly exhale. Nothing like this is planned in the game.
This was told by the creative director of the shooter Hugo Martin. He dispelled all doubts about microtransactions and the in-game store in the comments on Facebook.
Separately, Hugo specified that in the game for $60 there can be no donations or microtransactions from free-to-play or mobile games. Having paid the money, the player must get a fully completed experience. Therefore, you can calmly ignore cosmetics if you wish, nothing will change from this.