Unlocking the bootloader is a part of the rooting process. Users need to unlock the bootloader, then install the TWRP using fastboot and then root the device using Magisk or SuperSu.

Install Fastboot on your Computer: Install Fastboot on your Windows/MAC/Linux from here. Steps: Unlock OnePlus 7 Bootloader Navigate to the folder where you’ve installed/extracted Fastboot drivers.

All you have to do is enable ADB debugging, reboot into the bootloader, and run the same “fastboot oem unlock” command that you’d use to unlock the bootloader on a Nexus device.