So in short, you connect your soundbar to your ARC port, and your video playback device to the 4k@60Hz port, and everything will work.

I've been trying to get my laptop to send audio over the HDMI output into the HDMI ARC input on a new amp. Didn't work with the 11yo v1.2 cable I'd been using but also doesn't work with the one ...

Also, to use HDMI ARC, both your TV and your audio system need to support it. In addition, HDMI ARC has certain limitations when it comes to supporting the highest-quality audio formats.