Valve, fortunately, has already codified a ban on advertisement in games sold and on the steam platform itself (The store page is curated by an algorithm fetching popular games or game genres desired by the player rather than advertisers) https://partner.steamgames.com/doc/marketing/advertising

Edit: There's an exception for cross promotions and in-world/in-universe assets (giving logos on a race car in a racing game as an example)