There is no reliable way. It is like saying that LLMs can only produce output that is tightly constrained and user cannot control it to go outside of these constrains. If that would be true, these companies could not even dream 1 trillion valuations.

The question is how do you detect those who do not comply?

To point out the completely obvious, the approach described in your link requires compliance on the part of the author.

Given that the author could already have just inserted the text “hey I generated this via AI”, I see absolutely no reason why they’d go to the effort of adding an “AI label”.

As an european, this screams classic EU move for me. It adds bureaucracy for the good actors and do nothing to the bad ones.