How can I set the phone so it requests to unlock the screen before starting up?
Earlier I had to unlock the phone so it starts up but now it boots without unlocking (and I didn't change anything in this regard, at least deliberately). (I bought it as used so I don't know how it was activated).
It seems that there was an issue described in the link provided by Firelord in the comment:
Don't get tempted by any app asking you to enable its Accessibility Service. It will change your encryption password to the Android default one allowing everyone to decrypt the "encrypted" data. The PIN you enter at powering on your device may not be used for encryption at all - without a warning given.
If you use encryption on your Android device, follow these steps now:
- Open up the Accessibility settings menu.
- If a Accessibility Service is listed there at the top, disable it.
- Change your screen lock PIN/password/pattern whatever to reset the encryption password. Make sure to tick the "Require PIN to start device" option.
These three steps reactivate the password request for powering up on Android 8.0.
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