LinuxCNC 2.9 Live image won't boot with MBR

Hello, I've been running LinuxCNC 2.7 for 8 years now and I've decided to upgrade to LinuxCNC 2.9 because it's a 32bit installation, and software support is no longer a thing, browser is barely working, no modern SSH keys support (cannot use github anymore) - so I decided to upgrade to LinuxCNC 2.9 by doing fresh installation.

The problem is that PC won't boot from USB. I used dd to copy ISO to USB - and it boots on my modern desktop, but it won't boot on that old PC.
Is it because ISO contains only UEFI and not MBR ? What is the solution here?