The main difference between Complete Protection and AFU relates to how quick and easy it is for applications to access the keys to decrypt data. When data is in the Complete Protection state, the keys to decrypt it are stored deep within the operating system and encrypted themselves. But once you unlock your device the first time after reboot, lots of encryption keys start getting stored in quick access memory, even while the phone is locked. At this point an attacker could find and exploit certain types of security vulnerabilities in iOS to grab encryption keys that are accessible in memory and decrypt big chunks of data from the phone.
Based on available reports about smartphone access tools, like those from the Israeli law enforcement contractor Cellebrite and US-based forensic access firm Grayshift, researchers realized that this is how almost all smartphone access tools likely work right now. It's true that you need a specific type of operating system vulnerability to grab the keys—and both Apple and Google patch as many of those flaws as possible—but if you can find it, the keys are available, too.
The researchers found that Android has a similar setup to iOS with one crucial difference. Android has a version of “Complete Protection” that applies before the first unlock. After that, the phone data is essentially in the AFU state. But where Apple provides the option for developers to keep some data under the more stringent Complete Protection locks all the time—something a banking app, say, might take them up on—Android doesn't have that mechanism after first unlock. Forensic tools exploiting the right vulnerability can grab even more decryption keys, and ultimately access even more data, on an Androi ..