Comment 19 for bug 1899308

Thank you @Thomas Schmitt (scdbackup) & @sudodus

Using today's Lubuntu groovy ISO 2020.10.12, I ran
(based on @sudodus' comment #15)
--
#!/bin/bash
  original=groovy-desktop-amd64.iso
  test -f test_mbr.iso && rm test_mbr.iso
  xorriso \
    -indev "$original" \
    -outdev test_mbr.iso \
    -boot_image any replay \
    -boot_image any appended_part_as=gpt \
    -boot_image any mbr_force_bootable=on
--
to create new 'test_mbr.iso'. It was written with
`sudo dd if=test_mbr.iso of=/dev/sdb bs=4M oflag=sync

it booted fine on (not impacted by this bug)

hp 8200 elite sff (i5-2400, 8gb, nvidia quadro 600)
dell [optiplex] 755 (c2d-e6850, 5gb, amd/ati radeon rv516/x1300/x1550)
dell [optiplex] 755 (c2d-e8300, 8gb, amd/ati radeon rv610/radeon hd2400 pro/xt)
(it appeared to boot slow on 755-8 or 2nd 755, but subjective)
dell [optiplex] 780 (c2q-q9400, 8gb, amd/ati cedar radeon hd 5000/6000/7350/8350)

HOWEVER it did NOT boot on

hp dc7700 (c2d-e6320, 5gb, nvidia quadro nvs 290)
hp dc7900 (c2d-e8400, 4gb, intel 4 series integrated i915)

Please feel free to verify what I did & highlight any mistakes.
(keep instruction dead-simple for me please)