I've read people say the 9.4 update (or a prior one) removed "leveling." For me,[1] it is in the * settings menu when watching a tv input. There are two audio menu entries. One is sound mode. The other is volume mode. Leveling (for me[1]) is in volume mode.
So, you may not have that option. Either way, I think the goal is to have sound mode = "normal." And, volume mode = "off." You don't want any processing/overhead. Just straight audio.
Something else you could try:
Clear the cache (fixes random reboots)
Hit HOME 5 times.
UP once.
REWIND twice.
FAST FORWARD twice. (Clears cache & tv reboots itself. Be patient. It takes 2-3 minutes for the tv to go black, and come back on)
There are people who have said this fixes a problem when other things don't. Nobody knows what it does (but Roku has gone the extra mile to assure us there is no cache, as if that's the important thing to focus on). But, I've seen people say it fixed a problem after other self-help "try this" advice didn't. It wouldn't hurt to try it. Just be patient. You might feel like your tv locked up. Resist the urge to intervene.
Another thing you could try: home>settings>system>advanced>factory reset. I think there's also some audio/video reset in there. You could try that. But, if that didn't do anything either, I would do the factory reset, but during the setup tell it you'll connect to the internet later. This brings the tv up with a minimal'ish software. To me, it looks older. The antenna tv interface works like it used to before 9.4. But, admittedly, this doesn't seem to fix other 9.4-induced problems. So, I don't know.
The idea here is: if you can watch something through HDMI (a game, a streaming device) or antenna tv, and see that the audio works ok, then go to home>settings>networks to create your connection. Then go to settings>system>system update to force it to check for an update. If the audio goes bad again, that might say something. (I don't know what you could do to fix it. Just that you could factory reset again, and stay disconnected from the internet, and stream through HDMI. At least get more use out of your tv this way.). You might explore that option.
[1] I factory reset my tvs, and didn't connect to the internet. That returned the "leveling" option to "volume mode." (Or, perhaps returned the volume mode to the menu list. I don't recall how it was before "cutting the cord 2.0" with Roku.). Some people want leveling back. Cutting the cord would be a way to do it. In your case, this doesn't apply to you.
"People are often amazed at how much we’ve done with the number of engineers we’ve got." (Roku CEO Anthony Wood, Austin Statesman, Oct 4, 2019). "Amazed" is one way of putting it.
