MacBook no longer mirrors audio to external screen when it is closed
I would recommend looking at the System Preferences/Sound/
Look for the available audio sources. If your available audio source is available, you might have to double check all of the volumes associated with the expected output. For example, the volume on my iphone changes if I play from the speakers versus a bluetooth device. 

Additionally, you might try connecting with airplay 2, just to see if the audio is actually getting to the television and if there is any latency, or the bluetooth version for this tv. 

I run my Macbook Pro's 2017 audio to a Bose S1 Speaker. I don't use an HDMI port to access the speaker but rather my bluetooth. There is no latency as far as I can tell. I have heard the airplay 2 for those televisions is pretty good.