The more full reason is that the device is still encrypted prior to first unlock and is harder to extract any information from. As to what you said about police requiring you to enter your PIN, they can’t. You can’t be forced to reveal your passwords/PINs but they can legally force you to unlock biometrics (fingerprint/face ID)

I’d be curious to see a citation because everything I can find suggests it’s still obstruction of correspondence and a federal offense as they were not the intended recipient

Onyx boox runs android. You could probably root it, but I’ve never looked into it