Grub failed during install

[tadeusz cantwell]

Having picked to replace the previous ubuntu mate install on a duel boot with Solus, a fatal error warning appeared because grub couldn't install.

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: ubiquity 21.04.14
ProcVersionSignature: Ubuntu 5.11.0-13.14-generic 5.11.7
Uname: Linux 5.11.0-13-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu61
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.461
Date: Sat Apr 10 00:20:36 2021
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu-mate.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Ubuntu-MATE 21.04 "Hirsute Hippo" - Beta amd64 (20210407.1)
ProcEnviron:
 LANGUAGE=en_IE.UTF-8
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_IE.UTF-8
 LC_NUMERIC=C.UTF-8
RebootRequiredPkgs:
 linux-image-5.11.0-13-generic
 linux-base
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)