Hi just seeing if you could help, I've followed your steps and im currently in boot loop after applying the LibreELEC-Generic.x86_64-8.0.1.tar update.
I have made the flash usb with the libreelec usb creator with the file LibreELEC-Generic.x86_64-8.0.1.img.gz and edited the syslinux.cfg so I'm able to boot in live.
but now have hit a stumbling block as I'm looking in file manager (if that's right) and I'm unsure what file I'm looking for (or where to find it) on the hdd to add the radeon.dpm=0, any help would be appreciated