[OnePlus 8 / 8 Pro & 8T Cross Device Development] dlads:
Ok so i flashed this badboy, very impressed by it's pace, such a snappy ROM, it's running like silk.

anyway i thought i'd make the guide to flash a little easier than whats described in the OP, the sideload alone could be confusing and be careful of what version you download; polaris and instantnoodle are both hosted there, you want instantnoodlep (i know most people know this but it could be handy to know what to look out for)

Anyway, heres the installation guide and root, i've opted for the payload method, plus i've uploaded the magisk patched zip for 11.0.6.6 with magisk 23 in use.

Download the recovery and Evo X files and place in ADB folder.

On your computer

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1. Connect your phone to your computer and open a CMD / Powershell terminal pointed to the ADB folder, mines in the root of C so c:\adb

2. Run this code: adb reboot bootloader - your phone will reboot to the bootloader

3. Run this code: fastboot flash recovery .\instantnoodlep-recovery.img and press enter

NOTE: you can search for the img by typing in it's first letter then press "Tab" so type in i then press "Tab", this will populate the command with the first letter beginning with whatever you typed i = instantnoodlep-recovery.img

On your phone

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1. Using the volume keys navigate to "Recovery Mode" and press the power key, youll then be in the custom recovery

2. Click "Factory reset" in the menu, then click format data (THIS WILL WIPE YOUR DEVICE, BE SURE TO MAKE A BACK UP BEFORE YOU DO THIS)

3. Once complete back out then click apply "Apply Update" this will open up the sideload feature, click "Apply from ADB"

On your computer

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1. Run this code: adb sideload "NAME OF ZIP" (again you can use the tab feature to find the file)

2. Once you press enter the process will start and it will flash thereafter, this will take a while (make a cuppa while you wait)

On your phone

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1. Back out of sideload and click "Factory reset" once more then format data

2. Finally click on Reboot now and the device will reboot, the first boot should be a lot faster than OOS, you'll know it's working as the boot sequence will be different

Rooting

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1. Download the relevant custom ROM and open the zip, you'll see a bunch of files, copy out the payload.bin file

2. Using the payload dumper program, copy the payload.bin file from your ROM zip to the "input" folder within your payload dumper folder structure

3. Run the payload dumper tool and it'll extract a bunch of images which will be placed in the "output" folder, we want the boot image (boot.img)

4. On your phone, enable developer options and install Magisk on your phone.

5. Copy the stock boot.img to the root of your phone /sdcard

6. Open Magisk and select the top "install" option on the main page

7. You should only have one option if you aren't rooted and that will be "Select and Patch a File" select this then choose the boot.img you copied over

8. Once patching is complete this will move the patched boot image to your "Downloads" folder, copy this out to your ADB folder on your computer

9. On your computer open a CMD / Powershell terminal window pointed to your ADB folder and type in adb reboot bootloader, your phone will reboot

10. Once in the bootloader type in fastboot boot "NAME OF IMAGE" in my instance the command was:

fastboot boot .\magisk_patched-23000_gwZZy.img Once you press enter the device will boot with this image in use

11. To make root permanent simply open magisk, then select the top install option, then "Direct Install"

12. Finally reboot and you're done, root should be permanent.