Problems withgrub installation on dual boot with windows

[Malcolm Hart]

grub-installer repeatedly fails.
Dell Inspiron 7506 with Windows 10
I have disabled secure-boot and created blank partition for ubuntu and swap.
grub-installer fails - I have tried installing in /, /boot, and Windows EFI partitions - all fail with same error.

I also tried boot-repair and got an error writing the grub*.efi file

pastebin: http://paste.ubuntu.com/p/8VXVxjSMPn/

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity 20.04.15.2
ProcVersionSignature: Ubuntu 5.4.0-42.46-lowlatency 5.4.44
Uname: Linux 5.4.0-42-lowlatency x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27.4
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.445.1
Date: Thu Jan 14 10:21:57 2021
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntustudio.seed only-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu-Studio 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 LANGUAGE=en_GB.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)