>>"something they have neither the ability nor the desire to do."

>100% they could add client side scanning, why do they think its impossible?

I think you've misread that sentence. It's saying that they don't have the ability right now, as-in this is not a feature they've written in their software, and that further they do not wish to do so (in the same way that Apple did not want to write a backdoor for the FBI previously). Obviously as a matter of programming of course backdoors can be written and have been. But software developers don't want to be forced at gun point to do so like the EU proposes, which seems perfectly understandable.

And fwiw with open source software it actually would be arguable that they "don't have the ability" on a more technical level since that couldn't actually be enforced on the users and the EU's jurisdiction ends at its borders. Obviously many of the most popular messengers are proprietary, but not all. And even for the proprietary vendors that probably does factor into their arguments, as it'd put them at a commercial disadvantage.

Perhaps its more along the line of it being impossible to have privacy if privacy invading scanning is required. Its impossible to have secure encryption if there is a requirement to be not secure so that every message can be read by any government that wants to.

What apps can access can be restricted by the OS.

All you need to do to avoid it would be to encrypt outside the app, something most people would not bother to do, but criminals would be motivated to do.

They can't do it without false positives stochastically decrypting perfectly legal conversations without a warrant or any sort of due process. Of course, the EU elites don't care, but the leadership of Signal/etc obviously do.