Is it possible to have a full disk encryption system with a dummy passphrase ?

(This is just a question that I had in mind, I don't plan on committing any crime)

In my country, it is a crime to not give your password in the case of a criminal investigation. So if your computer disk is encrypted, you would have to give the decryption passphrase.

Would it be possible to have software that encrypt your disk but also allow for a "dummy passphrase" to be used ?

1/ if you use the correct passphrase, …

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