new dual boot install (win10 + Ubuntu 20LTS) crashes while installng grub

[Floris]

HDD with MBR
originally windows 10 PC, installing Ubuntu 20 on the side.
partitioned 500GB HDD with Gparted.
original partitions:
sda1: 500MB NTFS, boot, windows reserved
sda2: 336GB NTFS, Windows OS+data, (shrunk to 336 GB during partitioning)
sda3: 548MB NTFS, msftres

new partitions:
sda4: 152.21GB extended
sda5: 111.67GB NTFS, intended for windows data
sda6: 25GB ext4, intended for ubuntu OS. mount point "/target"
sda7: 15GB ext4, intended for /home
sda8: 550MiB fat32, intended for EFI. mount point "/target/boot/efi"

Since the install failed during GRUB install, at this point hoping my windows will still boot....

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
Date: Sat Aug 19 21:43:36 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)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)

[Floris (fgjzoet)]

Ubuntu installer required me to create an EFI partition to install Ubuntu. However the parition table is DOS ie MBR ie legacy. Ubuntu Installer could have checked and known this, but like indicated, explicitly asked for an EFI partition.

Since grub tried to install on EFI, this probably conflicts with the legacy MBR setup.

I suspect the cause of the bug is Ubuntu installing itself as EFI on an MBR drive.

The Ubuntu installation medium obviously was made on a different PC however that should not have mattered.