Hello AED226,
After reviewing your post, it sounds like you are able to play sounds trough other connected displays, but not through this one specific connected display.
"On your Mac, choose Apple menu
> System Preferences, click Sound, then click Output. If your Mac has only one audio port, click the “Use audio port for” pop-up menu, choose Sound Output, then make sure your external speakers are selected."
"If your external speakers still aren’t working, check the instructions that came with your speakers."
If you can’t hear sound from your Mac speakers
Change the sound output settings on Mac
Please don't hesitate to let us know if the steps resolved your issue or if you need additional assistance.
Thank you for using Apple Support Communities. Have a nice day.