Ruling: Thumbprint scan is like a "blood draw or fingerprint taken at booking."
The legal situation is more complex and nuanced than the headline implies, so the article is worth reading. This adds another ruling to the confusing case history regarding forced biometric unlocking.
In order to turn off the Find My iPhone functionality, you need the Apple ID password, so this isn’t even a real concern. You can even remotely lock the phone with a new password. Apple has made stealing an iPhone and making it work afterwards very hard.