I input EFI\ventoy\ventoy.json to write
{

"theme_legacy": {
    "display_mode": "serial_console",
	"serial_param": "--unit=0 --speed=115200"
},

"theme_uefi": {
    "display_mode": "serial_console",
	"serial_param": "--unit=0 --speed=115200"		
}

}

is not work.

Ventoy-LiveCD doesn't support serial console.
Why you need serial console? You can use VirtualMachine with LiveCD to install Ventoy.

Ventoy-LiveCD has DD format Function ,I want to use it to dd OS.

@ventoy Not sure about ystartgo but I need to use serial console because my router lacks VGA.

(Actually, I successfully booted it in that blind mode and installed OS on it, but it would be nicer if I saw the menu.)

+1 please consider support serial console. Some industry products have no VGA output.