The FTC would seek to force MS to sign something saying "If you let us buy Blizzard, we will sell the game on Steam/Epic/MS Store on equal terms". Distribution is a great chokepoint for a monopolist, so the agreement would (theoretically, since it never works out in practice) take that away from MS.

I don't personally think the FTC is going for a consent decree here though, Lina Khan is about antitrust, I think they are trying to block mergers as a matter of business.