Cellebrite isn't definitionally lawful. It's a private company that sells to other private entities that may or may not choose to use their software lawfully. I don't think they (should) get a pass just because some of their clients happen to be LEO.

You're going to have a long way to go to claim that Signal publishing files onto hundreds or thousands of devices is obstruction of justice.

The law doesn't look kindly on prior restraint.