What model TV do you have? Are any other devices connected to the TV?

My TV is an LG OLED CX 65, without connection to any other device. Thank you

Try this:

Disconnect everything from the TV and unplug the Arc and TV from power for a couple of minutes. Plug everything back in but keep everything disconnected. Make sure Simplink is enabled in the TV settings. Run TV Setup in the Sonos app and follow the app instructions. When the app instructs you, connect the Arc to the TV’s HDMI ARC/eARC port using the Sonos-supplied HDMI cable.
 

And set your TV to these settings:

HDMI Input Audio Format: Bitstream

Digital Sound Output: Pass Through

eARC Support: On

I have rebooted the entire system and now it seems to work