There are already existing laws to compel one company to do business with another, in America and in the EU, even before DMA... I think in the US it's refusal

There are already existing laws to compel one company to do business with another, in America and in the EU, even before DMA... I think in the US it's refusal to deal. And the EU can make companies do _anything_ they want to, within the jurisdiction of the EU. If they want to ban phones that are coloured green then they bloody well could, with the repercussions being fines, legal action and bans from the market.