[G4 Q&A, Help & Troubleshooting] steadfasterX:
> => I haven't managed to work out how to access unencrypted data partitions on a HDD on the laptop I'm using (Windows is on NVMe SSD)

open the file explorer and you should see your windows disk in the left panel. click on it and it should mount (asking for the FWUL/mAid login password which is always: "linux")

> => I copied the h815_20p_ARB0_0314.kdz file onto the USB drive that I'm booting FWUL 3.2 forgetful from, but couldn't see it in FWUL file manager...

the USB stick is fully managed by the OS and so you cannot use it to copy data etc. use another stick or usb hdd disk or access your windows drives (see above)

> => I still don't see an Extract + Flash option in SALT - should I..?

yes and no. The "Extract" button for KDZs is there always. Flashing not. SALT is not meant to be used by the average user to flash. there is a way when needed but as it is dangerous it is not enabled by default

> SALT gives these details re the phone:

> Device model = LG-810

> Firware (laf) = H81010o

yea congrats! you have won.. this is a so called "Frankenstein" device! Pls take the time to read UsU FAQ #21. when SALT shows h810 like it does it is at 95% a H810. to be 100% follow that FAQ but usually it is as it is shown.

this is bad in many ways: no one actually can say what the guy did with your phone, for sure flashing another bootloader stack to make it boot etc. but what else? nobody then that human knows. this can have a lot of site effects later!

> LAF protocol: 1000001

that means you could use SALT for flashing if ever needed. if you flash MM for example this will increase to a higher number where SALT cannot flash anymore

> AntiRollBack: 20 (not sure if that was 2.0..?)

you have to switch to "develop" in SALT (thought I had said that?!). Read the SALT faq how to do that. After that the ARB should show up correctly (in your case just "2").

this ARB + model and LAF firmware all together results in 100% that this device is NOT a h815. if its really a h810 stays at "only" 95% though ;)

> - Does the fact it's actually an H810, with ARB 2 explain why I haven't been able to update firmware..?

yes

> - Do I have to unlock now to be able to update..?

the h810 (assuming it is one) is not able to unlock officially. the only avail method is by UsU. If you want to go with a custom ROM then its your only option. If you want to stay stock.. well hard to say. as said above anything you do normally to a G4 might not work or break things in a Frankenstein.

For example you could try flashing a H810 MM ROM and see if LGup let you do that or not. again that might make things worse and now that it is clear that your ARB is blown (never the case for a h815) you have to ensure that you do not flash any ROM with a higher ARB then 2. Otherwise you will not be able to unlock by UsU if you ever want to do so.

as you can see there are no clear instructions how to proceed. all depends on your own risk level and what you actually can live with. assuming the device is a h810 you could unlock with the h810 UsU files and then work with that device as it would be a h810 (i.e. flashing h810 ROMs). Will you have any issues that way? No idea.. its a Frankenstein ;)

in any case I would recommend before doing ANYTHING ELSE - regardless of what (UsU or not, other stock ROM versions etc) - DO A SALT BACKUP! Start SALT -> Backup -> Basic. This contains all required files needed for restoring essential parts of the system (e.g. bootloader, modem etc) but not the Android ROM itself. If you wanna backup that too choose "custom" and select everything except "userdata" and "cache". that one will take way longer obviously and you need enough disk space ofc. again it is good having access to your windows drive or if that does not work another USB stick/disk.

Last but not least: SALT -> Advanced menu -> Debug log -> UPLOAD button: this is the most easiest way to share the SALT log which is a good idea usually.