[Nokia 6 Guides, News, & Discussion] hikari_calyx:
You can download the required firmware I mentioned there:

https://xdaforums.com/nokia-6/how-to/nokia-6-ta-1000-homebrew-stock-android-t3752006

PART 1: Preparation

1. Install OST LA 6.0.4 and patch it. DO NOT INSTALL OST LA 6.1.2 I MENTIONED BEFORE.

2. DO FULL BACKUP, DO FULL BACKUP, DO FULL BACKUP!

PART 2: Downgrade bootloader

To downgrade the bootloader, you need to download this OTA package:

https://ota-filesite.c2dms.com/SWUpdate/500000748

To prevent from FIH removed this OTA package, I mirrored this OTA package.

You need to enter stock recovery manually.

In some cases, you may get stuck at stock recovery.

Pick "Install update from ADB", then use adb sideload command to push this OTA package to your phone.

adb sideload D1C-331G-0-00CN-B01-331F-0-00CN-B01-update.zip

After this update installed, your phone will reboot once, then get stuck at recovery. Your bootloader has been downgraded now.

PART 3: Install homebrew "Stock" firmware

Download the firmware from the link above.

D1C-331G-0-00CN-B01.7z - Nougat 7.1.1 with December 2017 Update

D1C-332A-0-00WW-A01.7z - (Hong Kong/Taiwan Variant, Full Google Play Service included) Nougat 7.1.1 with July 2017 Update

D1C-5210-0-00CN-B03.7z - Oreo 8.0.0 with January 2018 Update and old bootloader

D1C-5550-0-00CN-B02.7z - Oreo 8.1.0 with March 2018 Update and old bootloader (made from leaked OTA)

Extract the firmware archive into a new directory, for example, I extracted it to D:\D1C-331G-0-00CN-B01.

Open OST LA from INSTALLATION DIRECTORY DIRECTLY. Load the mlf file in extracted directory.

If your phone get stuck at recovery, pick "Reboot to bootloader", then connect your phone to PC.

If your phone is already powered off, just connect it to PC directly.

Click "Next" if it's usable. Otherwise, click "Edit Phone Information", after "Boot FTM Mode Fail" prompts, you can click "Next" now.

This will flash the firmware to your phone. If the procedure unexpected interrupted because of your phone doesn't cooperate properly (e.g. Your phone suddenly reboots to OS), close the OST LA, then press and hold both Volume keys and power key to force power off your phone, then flash it again.

When the progress bar is going to complete and your phone is booting (NOKIA logo is displayed on the screen), the flash procedure is already completed.

In most cases, if your phone prompts md5 checksum fail after flashing, this is also expected. You can close OST LA, unplug the phone, then reboot the phone with [Volume Up] and [Power] key.

PART 4: Full userdata erase

Because the encrypt algorithm is different between Nougat and Oreo, you must do full userdata erase or the phone will get stuck at NOKIA logo.

Enter Download(Fastboot) mode again with the method you're familiar with.

Open OST LA, load the firmware, then click "Edit Phone Information".

If you've already know how to obtain the service permission, you can just type this command instead:

fastboot oem dm-verity (md5 checksum of your phone's serial number)

Then type this command:

fastboot format userdata

You also need to flash TWRP to do another format procedure, which the procedure I've given in this topic:

https://xdaforums.com/nokia-6/how-to/guide-how-to-flash-custom-recovery-root-t3702354

After you enter the recovery, tap "Wipe" (清除), "Format data partition" (格式化 Data 分区), then type "yes" to proceed.

You can reboot your phone to the OS now. If the phone get stuck at Powered by Android logo, just do PART 3 again.