Is it impossible to install legacy boot? Is efi compulsory? I have not found a way to install on older computers.

[Raymond]

Grub constantly fails to install on legacy boot systems

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: ubiquity 20.10.11 [modified: lib/partman/automatically_partition/question]
ProcVersionSignature: Ubuntu 5.8.0-23.24-generic 5.8.14
Uname: Linux 5.8.0-23-generic x86_64
ApportVersion: 2.20.11-0ubuntu50
Architecture: amd64
CasperMD5CheckResult: pass
CasperVersion: 1.452
CurrentDesktop: KDE
Date: Sat Oct 17 08:49:29 2020
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/kubuntu.seed maybe-ubiquity quiet splash ---
LiveMediaBuild: Kubuntu 20.10 "Groovy Gorilla" - Beta amd64 (20201016)
RebootRequiredPkgs: linux-image-5.8.0-23-generic
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Jordan Williams (jwillikers)]

Same here. My laptop only supports legacy BIOS, no UEFI. The installer won't load by itself. I worked around this with Ventoy, which supports legacy BIOS by default, and booted the installer from there. Of course, restarting after the installation just leads to the BIOS outputting "Operating System Not Found" making my workaround completely useless.