Data isn’t overwritten like that. The keys are deleted so the encrypted data is inaccessible.

And if people want a decoy, they can use a profile. I’m not sure why GrapheneOS has to add a feature for something that can already be done.

You cut out 90% of the security issues when you replace it with Lineage.

That’s not true.

The duress PIN/password feature as is makes getting data off the device impossible. The decoy profile approach means handing an unlocked device over to someone with access to forensics software. They can see the other profiles, logs if they’re still around, and other general data. If the profile’s session was ended, they’d need to unlock it to access the data, but since they’re already logged in there’s a much bigger attack surface. Maybe it would make it easier for them to exploit the secure element and bypass throttling, for example. It’s better to not unlock the device at all, even better if it had rebooted.

It’s more complicated than that. Forensics software can get related data easy enough. Logs and other data will still be there until a reboot. If the device is rebooted, there is the hash that makes it clear it’s GrapheneOS + a huge hard to miss triangle grabbing attention. Developer options is only available in the owner profile, so using another profile for that would be obvious too.