"For Signal, Chat Control is also an existential threat."

Perhaps it would not be if users could write their own clients and run their oown servers

Perhaps the commercial third party intermediary model of "private" and "secure" communication over the internet (cf. the free, open source, peer-to-peer model) is fundamentally-flawed. This is the model where a third party like Meta or Signal controls the software and requires connections be made to its servers in order to communicate over the internet. It is not an internet service provider, it's just a middleman trying to attract internet subscribers to use its software and connect to its remote servers

Perhaps this proposed legislation is simply leveraging that fundamental flaw

Acording to the latest draft I have seen, "Chat Control" does not attempt to regulate peer-to-peer communication, it does aim to stop internet subscribers from encrypting messages and sending them across the internet. It aims to regulate third party intermediaries providing "messaging services" to the public

The proposed legislation leverages the "centralisation" or "intermediation" of "private" messaging (the opposite of peer-to-peer) in Silicon Valley companies