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.

Once that’s done, type in adb reboot bootloader, which reboots your bootloader, and then fastboot flashing lock_critical, which prompts your phone to bring up the bootloader unlock screen.

Bootloader unlock Minimal ADB and Fastboot B. Enable developer mode – On your device, go to Settings and select About Phone, over there tap MIUI Version seven times, this would enable developer ...

To unlock your Sensation, you’ll need to download the Google Android SDK to run the fastboot command and request an identifier token.

Once entered, you will see the option for unlocking the bootloader pop up on your Pixel or Pixel XL. Like I said, it’s pretty straightforward, so long as you have experience using fastboot and adb.

After that, you may need to wait a few minutes, but the OEM unlocking toggle in dev options should become active. Toggle it and reboot into the bootloader. You should be able to use the "fastboot ...

That's no problem for an experienced Android user... except that they need to unlock the bootloader in order to access fastboot and re-install an older build or try a custom ROM.