The irony here is that simple one-time-pad solutions (OTP) will continue to be available to securely encrypt the sort of messaging that's of use to terrorists (relatively short infrequent messages), instead it's the general communications (including for banking) that the rest of us perform online that will be made vulnerable.

You don't even have to program or use a computer to create these OTP solutions, for limited messages you could just flip a coin to create the OTP if necessary (although there are lots of more automated solutions available as well.)

Airgapped computers at both ends provide another way 'round restrictions for more sophisticated actors. Their backdoors won't be accessible (remotely.)

So taking away secure encryption from the rest of us is just security theatre; a destructive, narcissistic legislative exercise designed to make it look like the pompous powerful doing something when they're doing nothing of any real use while creating terrible risks.

This is why, I think, legislators have consistently ignoring logic and math from professionals such as the OP - they don't care. They know perfectly well they're pissing into the wind doing nothing useful; that it's all theatre; they just think the fallout is going to land on someone else's pants after they're out of office. But tech works (and fails) faster than that.

[Counterargument: if everything else is breakable, securely encrypted messages really stand out. One answer: But very short messages (in an unknown format) aren't generally breakable, anyway, and that's the likely case.]