You should set as follows:
Code:
{
conf_replace_legacy": [
{
"iso": "/ISO/ubuntu-20.04.1-desktop-amd64.iso",
"org": "/isolinux/txt.cfg",
"new": "/Menus/Legacy-20.04.cfg"
}
],
conf_replace_uefi": [
{
"iso": "/ISO/ubuntu-20.04.1-desktop-amd64.iso",
"org": "/boot/grub/grub.cfg",
"new": "/Menus/ubuntu-20.04_grub.cfg"
}
]
}