The eARC is a feature implemented in the latest HDMI 2.1 specification, the biggest advantage is that it exceedingly improves bandwidth and speed.
This allows you to transmit high-quality audio from your TV to your Soundbar or AV receiver and is compatible with the high bitrate formats Dolby Atmos and DTS.

This documentation will guide you how to recored audio from eARC.

In order to use the eARC functuion, you need to make sure your TV supports the eARC function, in generic, if the HDMI slot on your TV has a eARC mark,
it means your TV supports eARC function, anyway you need to check with your TV vendor whether it supports or not.

You also need to enable the eARC function on your TV if it supports, you can check with the TV vendor about how to enable it.

You also need to enable the 'eARC' RX function on VIM3L, you can follow the command below to enable 'eARC' RX.

amixer cset name='ARC eARC RX enable' 1

You can follow the command below to check the status of eARC.

khadas@Khadas:~$ amixer cget name='eARC_RX attended type'
numid=24,iface=MIXER,name='eARC_RX attended type'
  ; type=ENUMERATED,access=rw------,values=1,items=3
  ; Item #0 'DISCONNECT'
  ; Item #1 'ARC'
  ; Item #2 'eARC'
  : values=2