[Shield Android TV General] ACiDxCHRiST:
(Note before you begin: If you have a SHIELD TV 2017, you will need a quality Male-to-Male USB Type A cable to connect your SHIELD TV to a PC. If you have a SHIELD TV 2015 or a SHIELD TV Pro, you may be able to just use a regular micro USB cable, because those two models have a micro USB port)

A. Download these files to your PC:

Download the Android SDK Platform-Tools

Download the Official NVIDIA SHIELD family Windows USB Drivers

Download the Magisk Manager APK (This is the latest version as of the time of writing)

Download the ***CORRECT*** NVIDIA SHIELD Experience Upgrade v7.2 Image for your model

(You will need to register for a Developer Account if you don't already have one. Flashing the wrong image will BRICK your device)

B. Setting up Android SDK Platform-Tools on your PC:

On your PC, extract the Android SDK Platform-Tools somewhere where you can find them

Add the platform-tools folder to PATH in the Windows System Environment Variables (Instructions HERE or HERE)

C. Installing the Official NVIDIA SHIELD family Windows USB Drivers on your PC:

On your SHIELD TV, enable developer options and debugging (Instructions HERE)

Using a Male-to-Male USB Type-A Cable, connect the USB port further away from the HDMI port on your SHIELD TV to your PC

On your PC, extract the Official NVIDIA SHIELD family Windows USB Drivers somewhere where you can find them

Open Device Manager and find the new device

Right-click it and select Update driver

Select "Browse my computer for driver software"

Input the path to the folder where you extracted the Official NVIDIA SHIELD family Windows USB Drivers earlier (make sure the "Include subfolders" option is checked)

Click Next and Install the Driver (if there is more than one option, select the one relating to ADB or Android Device Bridge)

Open a Command Prompt and type:

adb devices

On your SHIELD TV, a prompt will pop up asking you to allow ADB access from your computer. Check the box to remember your selection and then Grant Access

On your PC, the Command Prompt should show the serial number of your SHIELD TV

(You may have to run the 'adb devices' command again since it may have timed out the first time waiting on you to authorize the ADB connection on the SHIELD TV)

Boot the SHIELD TV into bootloader/fastboot mode by typing the command:

adb reboot bootloader

(Alternatively, you can enter bootloader/fastboot mode by following the instructions HERE)

On your PC, open the Device Manager again and find the new device (it will probably have an error with a yellow triangle)

Right-click it and select Update driver

Select "Browse my computer for driver software"

Input the path to the folder where you extracted the Official NVIDIA SHIELD family Windows USB Drivers earlier (make sure the "Include subfolders" option is checked)

Click Next and Install the Driver (if there is more than one option, select the one

NOT

relating to ADB or Android Device Bridge)

Open a Command Prompt and type:

fastboot devices

The Command Prompt should show the serial number of your SHIELD TV

D. Unlocking the bootloader on your SHIELD TV (CAUTION: THIS WILL WIPE YOUR DATA AND FACTORY RESET YOUR SHIELD TV)

Plug the NVIDIA SHIELD TV Game Controller or a USB Keyboard into the USB port closest to the HDMI port on your SHIELD TV

In bootloader/fastboot mode on your SHIELD TV, select "Unlock Bootloader", read the message and confirm

(Use the Y and X buttons to scroll UP and DOWN, and the A button to CONFIRM selection, if your button presses aren't doing anything you need to reboot the SHIELD TV into bootloader/fastboot mode with the Controller or Keyboard already plugged in)

On your PC, open a Command Prompt and reboot your SHIELD TV to the OS by typing:

fastboot reboot

This process only needs to be done once per device and you will not have to unlock the bootloader again for subsequent updates

(From now on while your bootloader is unlocked, your SHIELD TV will display a warning message when it first boots saying that the system cannot check for corruption. This is perfectly normal and the boot process will resume automatically after a few seconds. There is no need to relock your bootloader unless you are selling the device or something. NEVER lock the bootloader if you have anything other than 100% stock full RECOVERY Image installed. Never even try it.)

E. Installing Magisk Manager on your SHIELD TV and Patching your boot.img

On your PC, extract the NVIDIA SHIELD Experience Upgrade v7.2 Image that you downloaded to somewhere where you can find it

Find the boot.img file in the folder that you extracted it to

Open a Command Prompt and type:

adb push boot.img /storage/emulated/0/Download/

Install Magisk Manager by typing 'adb install [path-to-magiskmanagerapk]' example:

adb install C:\MagiskManager-v6.1.0.apk

On your SHIELD TV, open Magisk Manager [Settings > Device > Apps > Magisk Manager > Open]

(The Magisk Manager App Interface is not designed to be operated with an Android TV Remote so I suggest you install the NVIDIA SHIELD TV app on your phone. Once paired with your SHIELD TV, the app has an option to let you use a virtual mouse to navigate and interact with your SHIELD TV. Alternatively, you can plug a USB Mouse into the USB port closest to the HDMI port on your SHIELD TV)

If Magisk Manager automatically pops up and asks you if you would like to Install Magisk, select Cancel

Make sure the "Preserve AVB 2.0/dm-verity" option is checked, and then select "Install"

Select "Patch Boot Image File"

Using the Virtual Mouse on the NVIDIA SHIELD TV remote app on your phone, or a USB Mouse, navigate to the "Download" folder on your internal storage and select the boot.img file that you copied over then click Open

Magisk Manager will take a few moments to patch the boot.img (pay attention to the message in the console about the path to the patched_boot.img - It should be "/storage/emulated/0/Download/patched_boot.img"

On your PC, in the Command Prompt type:

adb pull /storage/emulated/0/Download/patched_boot.img

F. Installing Magisk rooted SHIELD Experience Upgrade v7.2 on your SHIELD TV:

On your PC, navigate to the folder where you extracted the NVIDIA SHIELD Experience Upgrade v7.2 Image

Find the boot.img and rename it to boot.img.bak

Rename the patched_boot.img to boot.img

Open a Command Prompt and type:

adb reboot bootloader

Once the SHIELD TV is in bootloader/fastboot mode, type:

flash-all.bat

(It will take a few minutes for the flashing process to finish and then the SHIELD TV will automatically reboot to the OS)

Optional Stuff and Additional Information:

Disable Auto-Upgrades by going to [Settings > Device > About > System upgrade > Auto-upgrade]

Enable Full OTA's instead of Partial/Differential by going to [Settings > Preferences > Developer options > Provide full system upgrades]

(It is the very last option at the bottom and this is very important when using a rooted device and modifications to the System partition are likely)

If you want to upgrade to a new OTA update with root without waiting on NVIDIA to post the Developer/Recovery images, the downloaded OTA file is in

/data/data/com.nvidia.ota/app_download

(You will need a root file explorer to be able to access this directory)

You can extract the boot.img from the OTA zip and patch it using the same method described in step E.5 through E.10

You can then install the OTA the normal way [Settings > Device > About > System upgrade > Check for upgrade]

(Make sure you have copied the OTA zip or extracted the boot.img to somewhere on your Internal Storage like "/storage/emulated/0/Download"

BEFORE you install the OTA

because the system will delete the file in "/data/data/com.nvidia.ota/app_download" when it installs the update and you will be unable to get it after that)

Copy the patched_boot.img that you made with Magisk to your PC

Reboot to bootloader/fastboot mode with:

adb reboot bootloader

Manually flash just the Magisk Patched boot:

fastboot flash boot patched_boot.img

Manually reboot back to the OS with:

fastboot reboot