What you can do: https://www.patrick-breyer.de/en/posts/messaging-and-chat-control/#WhatYouCanDo
Contact your MEP: https://www.europarl.europa.eu/meps/en/home
Edit: Article linked is from 2002 (overview of why this legislation is bad), but it is coming up for a vote on the 19th see https://www.patrick-breyer.de/en/council-to-greenlight-chat-control-take-action-now/
And if an app like Signal bypasses blocks, having it installed could become a crime.