Government mandated spyware
To give an example: based on this proposal an instant messaging platform can be given the task to detect material of the sexual exploitation of children. That could be known material, or "new" material, or grooming, so text. Let's assume, for the sake of the argument, that the order is given to Meta with regards to Whatsapp. A platform that, as you know, is protected with end-to-end encryption. This type of encryption means Meta can see who is communicating with whom, but is unable to read the content of that communication. But how is Meta supposed to detect something in a conversation it's not supposed to be able to access? For the sake of convenience, the Commission leaves that decision (the "how to do it") to the platform. Our guess is that the only way to do it, is by installing some sort of (now, government mandated!) spyware on the phones of the people using a particular service. After all, that is the only place where the content of the chats is readable.