Installer created unbootable LMDE6 on legacy BIOS PC

[dftf-stu]

Hi all

Firstly, apologies if this isn't the correct place!

Ahead of Windows 10's retirement, I've been testing Linux on an old BIOS-only PC, by swapping-in a different SSD.

I first tried MATE and XFCE, but they each had an issue -- post-install, I can only boot into the OS by choosing "Boot from local drive"
from the DVD start-up menu. Otherwise my laptop errors, saying the drive is unbootable.

I looked-around online, and apparently this is an upstream bug in the installer derived from Ubuntu -- so I remembered the LMDE
version, which I believe isn't derived from Ubuntu, and thought I'd try that.

Alas, same issue... "drive unbootable", unless I let the DVD boot, then pick "Boot from local drive". Then it boots the OS, and it works
fine once loaded, with decent performance.

This is the partition layout the LMDE6 installer created:

• /dev/sda , MBR , 2.1 MB , unallocated space
• /dev/sda1 , MBR , 8.5 GB , Swap (Version 1) - active
• /dev/sda2 , MBR , 492 GB , Filesystem root , ext4

And for comparison, what MATE or XFCE installers create:

• /dev/sda1 , GUID , 1.0 MB , BIOS boot
• /dev/sda2 , GUID , 538 MB , EFI system /boot/efi , FAT32
• /dev/sda3 , GUID , 500 GB , Filesystem root , ext4
• /dev/sda , 1.1 MB, Unallocated space

Is it not-possible to boot the latest Linux Mint versions on pre-UEFI systems?

(By-contrast, Windows 11 does work using the DVD installer -- it creates partitions in the order: "boot", "system", "recovery".
However, it doesn't work when installing via a USB drive -- then it puts the boot-loader onto the USB drive itself! 🙃)

Have screenshots of the layouts from the "Disks" app, if they'd help?

Thanks