I have yet to find volume control possible with the TV remote for the usual setup of optical out to some bluetooth transmitter. I can't guess how you accomplished this but hey, I haven't seen this work for decades.

As to the factory reset there are caveats here. In a few TVs with analog out I have to find the menu for (and mind you not all TVs have this) that output and change the TV audio to Stereo or PCM along with another that usually reads something like "fixed level or vary with remote."

Since I have no access to this model I can only suggest the above and if Sony can't return it to how it worked proceed with a full return and refund as they broke it.