instalation of 20.10 using USB post install GRUB instal failed

Tried many times. Tried re-downloading and installing ios on SDCard. Tried 2 x new SDCards, tried to fix with Boot Repair post install... always the same. PC uses Rampage V board set to only UEFI, no security and no fast boot as instructed on Ubuntu Forum

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubiquity 20.10.13
ProcVersionSignature: Ubuntu 5.8.0-25.26-generic 5.8.14
Uname: Linux 5.8.0-25-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.455
Date: Sun Feb 7 12:32:01 2021
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 20.10 "Groovy Gorilla" - Release amd64 (20201022)
RebootRequiredPkgs:
 linux-image-5.8.0-41-generic
 linux-base
 linux-image-5.8.0-25-generic
 linux-base
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)