Hmm..... I went over the LG's Owners Manual and really didn't see much of anything helpful.... In fact, the connections, controls and audio sections, all seemed vague and incomplete.
The Manual did say, that the LG can receive Audio over HDMI and USB-C. But because it lacked any real detail on Audio Input, I'm left wondering if there is an OnScreen way to switch the Audio Input between HDMI and USB-C Input connections.
The only other thing that might help, is to download the the Mac OS OnScreen Control and the Dual Controller from > https://www.lg.com/us/support/product/lg-49WL95C-W.AUS to see if either of those help.
Or optionally, see if you can patch the Audio thru a USB-C to USB-C connection, along with the display's downstream USB ports.