You say you have tried everything, but haven't listed what everything is.
Have you tried restarting the TV?
Press the power button on the remote for 5 seconds and then click on Restart on the screen.
If that didn't work have you tried a power cycle?
Turn off TV, unplug, wait for 2 minutes, plugin and power up.
After updating the firmware did you check the Bravia Sync Settings and the Audio Output settings
in case they have changed after the update.
Are all cables seated correctly?
Is there any interruption to the sound on the TVs internal speakers
Have you power cycled the Soundbar?
If you think you have tried everything consider doing a factory reset, unless you have already tried that.
Make a note of all your app sign ins and passwords beforehand.
Although I have a different model of Sony TV it runs the same firmware version as your TV (v6.6780)
released on the 6/12/2023 and my TV does not have the issues you are experiencing and I don't remember
these support pages being inundated with posts regarding sound issues from those who updated to this version.
So it looks like it is an issue particular to you, so check and check again all the settings, cables and other variables
in your system.
Have you considered it may be a problem with the Soundbar, can you check the soundbar with another TV?
If you have exhausted all avenues to try getting the sound to work as you would expect then perhaps you have a hardware problem on the TV. Is it still under warranty if so make a phone call to whoever sold it to you.
