The AC7012 USB-C to HDMI dual monitor MST female adapter has to be connected to a USB-C port that supports Display Port Alt Mode (DP Alt Mode).
If the port has DP Alt Mode, then MST will be supported and you can use the AC7012 adapter to connect two monitors. The two monitors are recognised as separate screens on your notebook/PC, therefore extended desktop can be used.
When you have a macOS device, the USB-C port supports Thunderbolt 3. This connection does not support MST Daisy-chaining! Resulting that the connected monitors will show a copy (clone) of the main screen, called SST (Single Stream Transport)