No one seems to want to own this at the moment. If there are no surrounds, I suggest that you use the TOSLINK audio connection. This is not quite as convenient with respect to ON/OFF for the TV, but audio is reliable. You'll need to train the remotes and ARC for IR Volume control.

Is there a cable box in the system?

There are CEC blocking dongles. I have not tried any. In a system with multiple inputs (cable, Blu-ray, etc.) that one box is mucking up the CEC. Inserting a CEC blocker in that path may help. Again, I have not tried this.

It's possible that you could set the SONY eARC OFF and use IR Volume control, but I have not tried this.

I'm considering developing a 3rd party CEC controller based on Raspberry Pi that will listen to CEC commands and issue correcting commands as needed. I don't know if this would be possible. It would be very boring if this solution was unique to each system or had to be updated after every end unit firmware update.