You must have missed something during initial setup. Try going back to initial setup and toggle some options.
just to simplify, when I go to Audio output on TV, there are only two options I see 1> TV Speakers and 2> Audio System. Now, this 'Audio system' includes Optical out from the TV and also the AVR connected on the eARC port. TV gives the preference to the AVR connected on eARC port when 'Audio System' is connected and I don't get the sound out from the Optical port on the TV.
The question would be, how do I send the sound output to Optical port on the TV, when AVR is also connected on eARC port at the same time. Turning off AVR doesn't work, the TV turns it back on as soon as I select 'Audio System' I can try checking CEC disabled so it doesn't turn it on, but then its there for a purpose of using only single remote to turn on all the 3 devices.
I started observing this only when AVR is connected to eARC, it wasn't the issue when it was not connected. I wish the sound output section on Sony had more options than just the two I mentioned, where I could exclusively select optical out.