Criminals have already been using alternative ways to exchange data for a lo.g time, especially those who are exchanging images and videos (such as CSAM) as everyday messengers are completely inapt for transmitting such large volumes of data. And these algorithms will yield a lot of false positives too.

And it is the wrong signal to authoritarian countries as it makes people and companies extremely vulnerable. As Markus Hartmann, Chief Public Prosecutor in the German state of North Rhine-Westphalia, said not long ago on chat control:

"From the point of view of information security there is to assume an increased risk [of hacking]. There is no special expertise [demonstrated by politicians] in this area with regard to the signal effect for authoritarian states."

[Original link in German, translation my own.]