From seeing the broad overviews of EU's DMA, I think most of it is very well thought out and sound. The area I think it completely faceplants at is the requirements for messenger inter-operability.
This is a nice idea in theory but IMO chats are like railroads, they're naturally monopolistic. When you try to make chat systems interoperable, prepare for a bunch of messages saying 'this message type isn't compatible with your client'.