I had the same problem. I read somewhere that CachyOS won’t boot from an ISO file and needs to boot from a USB that has had the ISO written to it. There are several distros like this. I use a Ventoy NVmE drive as well normally but some distros have to be written to the USB - old style. I normally just use the built-in USB writer, in fact, I booted Mint from Ventoy and used the live system to write the CachyOS ISO to a different drive.