Diagnosis
This is almost always an audio format mismatch. Your PS5 is likely outputting a sound format (like Dolby Atmos or DTS) that the TV's internal speakers can't process directly over HDMI.
How to Fix It
You need to change the sound output on your PS5, not the TV. 1) On your PS5, go to Settings > Sound > Audio Output. 2) Set "HDMI Device Type" to "AV Amplifier." 3) Under "Audio Format (Priority)," change it to "Linear PCM." This sends a simple, uncompressed stereo signal every device can understand. 4) Switch back to the TV input. You should have sound now.
If That Didn't Work
On the TV itself, press the settings button. Go to Settings > Sound > Advanced Settings > Digital Audio Out. Change this to "PCM" as well. Also, check that "Speakers" is set to "TV Speakers" and not "External" or "Off."
Heads Up
If you later connect a soundbar or receiver via the TV's eARC port, you'll want to change these settings back (to Bitstream or Auto) to get the high-quality formats. The internal speakers are the limiting factor here.