Why can't I access the security option when my ASUS Flying Fortress is turned off (I just restored the factory settings and formatted all the hard disks win 10)?

Press and hold the shift key, and forcibly switch the machine on and off for 2~3 times. It will automatically enter the winRE interface when it is turned on. Select enter safe mode through troubleshooting-advanced options-startup settings-restart.

If you can't enter safe mode, you can reinstall the system yourself or go to the service center to restore the pre-installed system.