guestDescription property
The VM's OS.
See for example https://vdc-repo.vmware.com/vmwb-repository/dcr-public/da47f910-60ac-438b-8b9b-6122f4d14524/16b7274a-bf8b-4b4c-a05e-746f2aa93c8c/doc/vim.vm.GuestOsDescriptor.GuestOsIdentifier.html for types of strings this might hold.
Implementation
core.String? guestDescription;