[ASUS ZenFone 6 (2019) Guides, News, & Discussion] slutexpress:
EDIT:SOLVED -- READ BELOW:

I finally got it flashed by following a few guides here which I will link, and try to break it down easier for someone else to come across and follow. I thought I bricked my phone (flashed LineageOS then rebooted, phone did not show anything on screen, full black screen) but after following a few guides I got it solved.

If you get bricked, or just want to follow a clean perfect install, please start below (Skip to step 2 if you are starting fresh, if you have soft-bricked your device start from step 1)

1. Bricked it and had to execute QDLoader 9008 fix again.

Tutorial is easier than it looks, do not fear, if you have soft-bricked your device and see a black screen, go ahead and go through the qdloader brick solution.

2. From factory recovery updated to Version WW-16.1220.1909.193.

If you have started fresh, I would highly recommend updating to the more updated firmware first. For me this worked, and I suggest updating to get a more current kernel, which may play better with Lineage OS install. To install a newer stock firmware linked above, download the ~2GB Firmware above, and save it to your Minimal ADB / Fastboot folder. Power off your device, after it has been successfully restored (if you bricked it) or you want to start off fresh and get the install right the first time. With your device powered off, Hold Volume UP and then Hold Power Button until the Fastboot menu appears. Use your volume keys to select Recovery, then press Power button to enter the STOCK Recovery (we are still on stock firmware with stock recovery). When in stock recovery select install from ADB. We are going to push the install via ADB (I tried dragging the firmware to the internal and selecting install ZIP and that didnt work).

Go into your Minimal ADB / Fastboot folder on your computer and open command prompt by holding Shift+Control and Right clicking and then selecting open command prompt here.

Now, enter the following command in the command prompt and hit enter:

adb devices

This command will show if any fastboot device is connected. If it doesn’t show, then please check the drivers are installed properly and try again.

If your device is listed, then type the command given below and press enter:

adb sideload File_name.zip

^^This will be the ~2GB Firmware file downloaded above

Wait until the installation process completes.

Once the installation process is complete, restart your device.

Done. You have successfully upgraded the Asus ZenFone 6 to the newer firmware, please continue.

3. Downloaded OTA 16.1220.1909.193 to 16.1220.1909.194, renamed it to UL-ASUS_I01WD-ASUS-16.1220.1909.194-1.1.1-user.zip and placed into root of internal memory.

When I disconnected USB cable (or rebooted, not sure), I was prompted with update notification. I have updated it. Either way, reboot your device if you don't see the notification, and look in your notifications to see something saying: System Update Detected Proceed with Update - and select it and update.

4. Now that your phone is 100% Updated with the newest firmware, let's follow another guide I found here:

I assume you're on a fresh Android 9 stock ROM, or just finished restoring your phone with the Flashall_AFT.cmd from this tutorial.

You should at least boot once on the system, and disable any PIN or password to unlock your phone (hence putting a default password for the FBE).

Download the latest OFFICIAL TWRP.x.x.img (which we'll use to boot on it), and it's installer to install it later (TWRP.x.x.zip) if you want to use it.

LineageOS installation steps :

Reboot to bootloader (=fastboot mode), connect to your PC and boot on TWRP :

Command:

fastboot boot TWRP.x.x.img

Once on TWRP, you can see that we're on slot A (Menu > Reboot). Now go to wipe > factory reset and then wipe system (technically I suspect this only wipes slot A, but do it anyway, don't worry about the errors!)

Now go to Install > flash the newest official LOS_latest.zip. What happens here is that the LOS installer will flash LOS on the inactive slot (slot B in our case). And will also install the LOS recovery (on both slots it seems).

Reboot to recovery : your phone automatically switches slots and will boot the LineageOS recovery (Don't fear, we don't need TWRP right now, just go along with this step) on slot B.

On the LineageOS recovery, do factory reset (which seems to be a full /data format in fact, thus removing any previous encryption AND all your data on internal storage). If you want to use Magisk, go to the recovery's install menu and sideload it now

Use code:

adb sideload Magisk-v20.3.zip

Now reboot to system. It might take a while (one or 2 loops in my case), but your phone should boot, or in some cases will end up on LOS recovery asking for a 'factory data reset' (then do it and reboot again).

Once booted on your LOS rom, you can define a pin or password to lock your phone (that'll be the FBE decryption password).

Now if you want to use TWRP, reboot to bootloader and boot again on TWRP.img (step 1)

From TWRP > Install > flash TWRP.x.x.zip (that is, the TWRP installer). It installs on both slots by default. If you had installed Magisk, you have to flash it again (because anything modifying the boot.img - like the TWRP installer in our case - will erase it).

You can now reboot to system and enjoy LOS