Displacement not work

I created a simple material with a displacement map but it doesn’t show either in viewport or in the material preview. I set the parameters as “Flat tessellation” as you can see from the screenshot, i’m working on MacOS 10.11 and UE 4.14. How can i make it work?

Thanks for any help

is not supported on Metal in Mac OS X 10.11 (El Capitan) - API support for this H/W feature was only added in macOS 10.12 and support for it will be added in a future version of UE4.