The HDMI ARC support need to be enabled from the configuration of your TV on the specific ARC supported HDMI port and your external audio receiver as well. Also most of the times it is required to enable the TV CEC support.

However there is no advantage of using HDMI ARC other than 1 less connection from TV to the audio receiver. Even though it is a HDMI connection, it can't pass through the high definition audio such as DTS-HD MA, Dolby TrueHD etc. So no different from using Optical output.

That's CEC functionality and not ARC..