dual boot installation windows 10 ubuntu 20LTS fails with grub

[Floris]

see previous report (this is a double). grub install /dev/sda fails

may be partition recognition problem. existing EFI may be NFTS

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity 20.04.15.2
ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27.4
Architecture: amd64
CasperMD5CheckMismatches: ./boot/grub/efi.img
CasperMD5CheckResult: fail
CasperVersion: 1.445.1
CurrentDesktop: ubuntu:GNOME
Date: Sat Aug 19 22:34:05 2023
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 LANGUAGE=en_US.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 LC_NUMERIC=C.UTF-8
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)