You are following Managing TLS protocol configuration for vSphere 6.5 (2147469) to disable TLSv1.0 and enable both TLSv1.1 and TLSv1.2 on 6.5b vCenter Server with an embedded Platform Services Controller.
When you run reconfigureVc update -p TLSv1.1 TLSv1.2 you receive the following error – vami-lighttp supports either pure TLSv1.2 or all TLS versions. Falling back to all TLS versions.
Note – This happens on the external PSCs (which are done last)
vSphere Update Manager
Platform Services Controller