They can fine apple and google for offering signal in their app stores, until nobody has it installed.

That doesn’t break your comms today - but later, you replace your phone, can you get a current copy of the app?

The idea isn't to break encryption, it's to have apps implement client-side scanning "pre-encryption".

Definitely wouldn’t break the encryption itself.

I think the way it could work is to send a letter to each of the messaging apps saying that they are now legally required to use the EU’s encryption keys and make the messages available to the EU.

Then they would make it so that the apps that don’t comply are not available in the app stores by pressuring google and apple respectively.

I think this is the reason why for example telegram is not end to end encrypted by default - as some regions require them to be able to access users info.

Software you’re using on your own wouldn’t be effected, but wouldn’t necessarily be legal either.

People who are technically savvy could get around it, but the vast majority of people just assume that their private messages are private.

Making it illegal to use "non-compliant" e2ee services and prosecuting those who does. Realistically, they couldn't, but could ban such apps in EU stores, making them less popular.

They can break encryption by stealing keys from your device, or by pwning your device, or by introducing backdoor into the chat client for every user.

The proposed regulation is about imposing requirements on service providers, as defined by the Digital Services Act, for messaging and other services, effectively requiring them to implement backdoors in their software.

Purely P2P communication isn’t affected.

No, but many political figures have proposed banning the distribution/possession/operation of tools (e.g. Signal, Tor) which can be used to circumvent surveillance.

The app that decrypts the message, will have the capability to provide that message, now decrypted, to the government.