Samsung Galaxy S7 Edge
Google App v220.127.116.11
Google App > Settings > Voice > '"Ok Google" detection' > 'From any screen'
This brings up the "Search by voice from any screen" setup wizard.
As soon as I tap "Get started", I see a message stating: "Can't use the microphone. Restart your device."
Restarting does not help.
This also happened in Android 6.x, before I upgraded to Android 7.0.
I can record my voice in Samsung's Voice Memos app without any issues.
Google App has all permissions (including Microphone) enabled.