Are you trying to enter Fastboot to or flash a custom ROM ?
How to Open Fastboot Mode on Asus ROG Phone 3: A Step-by-Step Guide how to open fastboot mode on asus rog phone 3
Use the to scroll through the top menu options until you see START or REBOOT . Press the Power button to confirm. Are you trying to enter Fastboot to or flash a custom ROM
Fastboot is a diagnostic and engineering protocol that allows you to modify the device’s flash partitions directly from a computer. Unlike Recovery Mode, which is menu-driven, Fastboot relies on command-line inputs from a PC. which is menu-driven