That's not what the law cares about. Being
able to encrypt stuff end-to-end, is not what is being targetted — it is not realistically possible. What is being targetted is millions of people getting private, true end-to-end secure communication with no content scanning of any kind through some service. Are you providing that service to millions like Signal is? This law applies. Are you the size of Meta and are you implementing some 'clever' two-component solution to sidestep this law? Expect legal trouble.
You can already install a mail client with PGP-support. Will K-9 Mail get in to trouble if a million users in the EU started privately exchanging keys and using GPG with K-9 Mail? Who knows. These laws are not about such practical details. This is about unlocking massive amounts of signal intelligence to do… who knows what, and those large communication platforms are juicy targets. All it needs is a law to coerce them to cooperate.
Don't expect reasonable arguments from the proponents of such laws, and don't expect to be able to avoid them for millions of users with clever tricks; you'll still fall foul of the spirit of the law, if not the letter.