[LG G8 Guides, News, & Discussion] SirOlive:
This might be completely unnecessary (mods feel free to remove if it is), but I see a LOT of misinformation regarding GSI ROMs and the G8. So. Here's a guide/FAQ for those wondering if/what is possible:

***I'M NOT RESPONSIBLE IF YOU BRICK YOUR PHONE, LOSE YOUR DATA, OR OTHERWISE DAMAGE YOUR DEVICE. IF YOU CHOOSE TO FOLLOW THIS GUIDE, THE FATE OF YOUR DEVICE IS IN YOUR HANDS, NOT MINE, NOT YOUR MOTHER'S, NOT ANYONE OTHER THAN YOUR OWN***

Prerequisites (yes, these are all NECESSARY. If you don't know how to unlock your bootloader or use fastboot, there are other guides here. Go find one.)

Unlocked bootloader (and the V50 engineering abl files as well as stock, plenty of guides here with download links)

QFIL/QPST

Basic Fastboot, ADB knowledge

BACKUP. I mean ALL YOUR DATA kinda backup. This WILL wipe your phone, do NOT come crying to me if you lose the last picture of your favorite sock. Not my fault.

GSI for Treble device (ab)

GApps (optional, but recommended)

Instructions to Flash via Fastboot

WIPE YOUR PHONE

Yeah, completely factory reset that sucker. Doesn't matter if it's through recovery, settings, or adb, just bite the bullet and restore factory settings. You can technicially flash without doing this first, but you'll still have to wipe it before any flashed ROM will run. Sorry.

Boot to EDL (NOT download, your screen should be black, dev manager should show QD Loader 9008 COMx)

Use QFIL to flash engineering abl file to both a and b slots - yes, all this work just for fastboot.

Reboot to fastboot!

I just unplug my phone, use power + vol- to shut phone off and then reconnect while holding vol-, but you do you.

In case you don't remember, your touch screen WILL NOT WORK during this time, even if you fully boot to system! Completely fine and normal, means you're on the right track!

Fastboot Devices should yield "LG850UM", also good!

Open cmd prompt from platform_tools, copy path to desired GSI while you're in there

Run these commands line-by-line:

fastboot format system

fastboot flash system *Path_To_GSI.img*

This is where I usually repeat the 2 commands and attempt reboot while I still have fastboot, whether or not it changes anything I have no idea, but it's never given me problems so why fix it if it ain't broke?

fastboot flash abl_a abl_STOCK.bin

fastboot flash abl_b abl_STOCK.bin

fastboot reboot

Ta-Da! Your shiny new ROM should be up and running. Use TWRP or any kernel manager (I like SmartPak) to flash TWRP, GApps, blah blah blah.

FAQ/Troubleshooting

Touchscreen still not working? Go back to EDL and load the stock abl bin files through QFIL, then reboot as normal.

You will likely be asked to input a password upon successful reboot, just enter your PIN/password, whatever you used to unlock your phone pre-flash

The cool things like QuadDAC and LG-specific tweaks will probably not work. Weigh your options before flashing.

Magisk comes pre-installed with most GSI's, just follow the prompts and you'll be just fine.

Don't want GApps? Just sideload desired apk's via ADB, or use the browser to search for them.

Can't I just use TWRP and make this whole process a lot simpler? Yep. But some of us don't have working TWRP or prefer using fastboot commands. This is for those people, don't hate.

Which ROMs work?? Not sure, haven't tried them all. Currently running HavocOS found in Treble GSI forum on here.

Help! I broke my phone! No, you probably didn't. It's advisable that you know how to emergency restore via LGUP prior to starting this process though. Please be specific as to what part of this "broke" your phone and why exactly your phone is "broken" if you're going to ask for help- "bricked device" has never helped anyone.

Rebooting is your best friend in this process, especially during the first boot. If anything starts to hang up or act funny, just give the phone a minute to catch its breath and, worst case, turn it off and back on again

As previously stated, this is probably pointless, but given all I see on the G8 forum is "no custom ROM" or "why bother trying to *insert idea here*", I figured it might help some folks out. I'm sure I left a few things out, feel free to correct or provide input as necessary.