I think you and most people in this thread have been mislead by the article because of the closing remark.

Beyond terrorism, the most dangerous pedophiles communicate on Telegram to exchange content.

But it isn’t the private stuff he is being prosecuted for though AFAIK (although it might have been reported by “traitors” within those chats).

Unlike Signal, there are public chat groups and channels and I presume these are the ones which got him into trouble for propagating illegal activity.

From another article…

terrorism, narcotic supply, fraud, money laundering, receiving stolen goods and others… he allowed an incalculable number of offenses and crimes to be committed, which he did nothing to moderate

The platform has faced issues of misinformation and hate speech, especially antisemitic speech following October 7, 2023.

No mandatory 2FA as far as I know.

Then how is the authenticity of a number tested by Signal?

Isn’t spoofing a phone number easy for scammers? If so, I don’t understand why there is (admittedly) so little spam on Signal.

Does Signal require 2FA upon registration? (I cannot recall)

If they are the only two options then it isn’t practical. Wouldn’t six characters be enough? One in 56,800,235,584 chance of guessing and brute force attacks could be avoided with a limit of 3 tries per hour.

EDIT: Or I could just content myself with the first 6 characters matching. I suppose there is my solution.

Definitely a UI issue because it is not clear what the user is supposed to do according to the UI.

Should I be sitting physically next to the person to confirm? Read out the gazillion character code to them over a regular phone call?