This very much depends on the state. Some state courts (California) have ruled that one can refuse a request to unlock a phone via biometrics, while others (Minnesota) have ruled that you do not have the right to refuse.

My understanding is that a passcode or PIN can be considered “testimony”, because you have to communicate this information, and testimony can’t be forced.

But biometrics aren’t always considered to be testimony, because it’s something you ARE.