Court documents obtained by Forbes revealed that the FBI may have a tool that allows accessing private Signal messages on iPhones. The documents revealed that encrypted messages can be intercepted from iPhone devices when they are in partial AFU (after first unlock) mode. In December, the Israeli security firm Cellebrite claimed that it can decrypt messages from the Signal highly secure messaging app. It is unclear which model of iPhone was accessed by the FBI either an iPhone 11 (whether Pro or Max) or a second generation iPhone SE.”]
Source: https://securityaffairs.co/wordpress/114551/mobile-2/fbi-access-private-signal-messages.html