Here I am again!
Reinstalled as you suggested. Miraculously, Mojave recognised Radeon VII right from the beginning. I did my Multibeast and Post-installation files homework and most things worked pretty good.
Audio didn't, so I changed the layout to 7 as suggested > rebooted and craaack
tons of lines of failed VRAM tests and audio problems (controlID: 17, coreAudioChannelID = 2 FRONT RIGHT oldValue 0x41)
I rebooted from USB and manaeged to reput audio layout at 16. Reboot and same problem. Now I don't seem to be able to reboot from USB either.
I attach latest EFI folder after Multibeast post-installation work, pic of error debug, snapshots of system specs after installation before multibeast and after multibeast. Hope they can help.
ADDITION. Also a nvram.plist file has appeared in EFI root folder. Attached below too.
ADDITION 2. If I put this EFI I zipped below in the USB's EFI and reboot I can actually access Mojave. I've copied this EFI in the place of the on in the SSD, rebooted, still same error about Audio..
Thanks for your amazing work
@CaseySJ and all the others!