ubuntu installation 20.04 with alternate option fails ( sharing windows ssd)

[lebb]

I have a built PC. Has a Z3 Gigabyte Motherboard. Windwos 10, intel i7, gtx1080. The brand new Ubuntu 20.04 (downloaded the day of its release, the checksum is ok) installer does not recognises it has windows installed. I searched online and found solutions ( disabling fast boot, run disk checks, disabling windows paging, disabling kernel dumps ) but still ubuntu installer does not recognises there is a windows installed. Tried with the alternate option, created the partitions alongside windows on the same ssd.

Tried, efi partition, swap, root. Tried fat32 mounted on /boot, swap and root. Tried fat32 mounted on /boot/efi, swap and root. But nothing worked. I get the following message. "grub-install /dev/sda failed" Fatal error.

I will try with another distro hoping that I can install it on this machine (i had good experience with fedora on troublesome pc) and afterwards replace it with ubuntu.

I do need windows on the same ssd, because work, and I dont want to buy another ssd because it should not be necessary...

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubiquity 20.04.15
ProcVersionSignature: Ubuntu 5.4.0-26.30-generic 5.4.30
Uname: Linux 5.4.0-26-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CasperVersion: 1.445
Date: Sat Apr 25 14:30:10 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz persistent file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)