i've inherited a vcenter+esxi installation.
In VCenter Server Appliance I can notice that it is guest managed, that it means that it is using open VM tools.
I don't think it is the standard for Vcenter installation.
In this case I can't update VM Hardware Compatibility to Match host using "Update" tab.
Modification of the virtual hardware version on the VCSA is not supported. Likewise you should not manually install any additional version of VMware Tools inside the guest OS of the VCSA. It has been guest managed and will stay the same.