Enable it as you did earlier. Go to Settings => About Phone and press 7 times consecutively on "Build Number".
but there(above screen shot) about phone is not even visible ,then how come he can enable the developer mode
Can you reboot the device to safe mode by long press the power key and hold the power off to accept the safe mode and then go to the settings>system>about device
if that works then better do the reset and hope it may fix the issue
@user1520881638007 as much as I remember, the About Phone entry in Android 10 is directly under Settings and not under the Settings => System sub-menu. So, instead of tapping "System", he needs to tap "About Phone".
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