It seems the reason companies are currently allowed to do this in the EU is because there was in 2020 a temporary derogation from certain provisions of the e-Privacy Directive.

But it was temporary, so it will expire in April 2026. With this new law the intention is to make that "voluntary detection" a permanent thing they allow service providers to do, as a norm. The providers still have the choice to not do it, so I don't think this affects services like signal, as far as I understand.