theprofessor
or a custom sequence
Assuming that you are referring to something similar as this:
Devices ... were able to boot in two modes. When only the power button was pressed to turn the handset on, they booted into a dummy Android home screen. But when the handset was switched on by pressing the power button together with the volume button, the phone booted to a secret, encrypted partition which facilitated secret communication ...
No, there is no such mechanism nor feature built into GrapheneOS. See our FAQ regarding Security and privacy - How is disk encryption implemented
... access your hidden ... with a password