If the device is branded with delivery apps (e.g., Glovo, Deliveroo), it is likely managed by a custom MDM (Mobile Device Management) system. Resetting may not remove this restriction.
adb shell am start -a android.intent.action.MAIN -n com.teslacoilsw.launcher/.NovaLauncher sunmi v1 unlock
: Release the buttons once the Sunmi logo or the Boot Recovery screen appears. If the device is branded with delivery apps (e