ShinRamen247 In Australia, devices such as Ghost, Anom etc are regarded as DECCD.
Does that mean GrapheneOS is a [Dedicated Encrypted Criminal Communication Device]? I guess anyone can be a criminal by setting up a duress PIN.
Intention matters a lot when it comes to the lawfulness of various acts.
As far as I know, GrapheneOS has not implemented the duress password functionality to help criminals or hinder law enforcement, but to allow GrapheneOS users to protect themselves from individuals that are unlawfully trying to get access to sensitive data on the device, i.e to protect activists and journalists working in repressive regimes. As such, the functionality in GrapheneOS should be entirely lawful, since it is not "for the purposes of impeding law enforcement access to information on the device".
These DECCD devices talked about are different, since they are specifically made for and sold to criminals.
Now, whatever technology you use, you are not allowed to commit crimes, nor to destroy evidence after you have been notified of being under suspicion of crime. So telling the duress password to a police officer who has arrested you and taken your phone may be illegal, since it would be destruction of evidence. But using the duress functionality for legitimate purposes should be entirely fine.
(I am not a lawyer, just an activist and security expert interested in law. This is not legal advise.)