Il Game Director di DOOM Eternal, Hugo martin, confirmed the total absence of microtransactions within the game.

Hugo Martin Doom Eternal

Just in these hours the developer, in response to a fan who was wondering about the issue on Facebook, wanted to be clear to avoid any misunderstanding. Not only, Martin has increased the dose by stating that the only "purchasable" items (note well, through experience points), they will be skin and others cosmetics irrelevant for gameplay purposes.

Eternal is a $ 60 game, not a FREE TO PLAY or a MOBILE TITLE: we are giving you a complete experience without MICRO-TRANSACTIONS, just like YOU EXPECT IT.

In short, in an era in which very clear economic models often and willingly interfere with the quality or mechanics present in a video game, DOOM Eternal seems to want to be a (welcome) voice out of the core.