How do I install Zima OS on a PC with legacy Bios only!

I have tried installing Zima OS on my PC with Legacy bios only and it will not install. I have tried rufus and balena etcher. When I install the USB and power on the PC to boot from USB the screen says that insert a valid usb or choose another boot device. I have tried two USB sticks. I understand that I can install this software from either EUFI or legacy Bios. Is this correct? If so how do I do it?

ZimaOS requires UEFI. Your motherboard needs to support UEFI boot mode.

From ZimaOS Readme/Getting Started

Getting Started

To boot ZimaOS, the BIOS needs to have UEFI boot mode enabled and Secure Boot disabled.

Next, we need to write the ZimaOS image to the “boot medium”, which is the medium your zima device or x86-64 hardware will boot from when it is running ZimaOS.