I recently had a customer reach out who was having an issue deploying the latest vCenter Server Appliance (VCSA) 8.x to an ESXi host that had a CPU that was no longer supported. After the VCSA OVA was uploaded by the VCSA (UI/CLI) installer, it fails to power on the VM with the following error message:
The Intel "VMX Unrestricted Guest" feature is necessary to run this virtual machine on an Intel processor
This problem is only observed with older legacy CPUs that do not support some of the modern CPU instructions that is expected by most workloads today. There is workaround for those that still wish to run on unsupported hardware, which may yield other unexpected behaviors, by adding a VM Advanced Setting monitor.allowLegacyCPU = TRUE
However, there is a chicken/egg problem that user was not able to add this setting before the VM was automatically powered on by the VCSA Installer.