Sonos states that its home-theater speakers connected over optical audio accept infrared remote commands for volume control. Remotes that transmit only Bluetooth or radio-frequency signals may not work until configured to emit IR. HDMI-ARC Sonos products can use different control paths, but that does not change the Playbar’s optical requirement.
This is a clean diagnostic distinction: audio playing through the optical cable does not prove that the television remote can control volume. If a Bravia remote is paired over Bluetooth, inspect the TV’s remote-control configuration and the Playbar’s Remote Control Setup instructions rather than assuming the optical cable is faulty.
What to do: read Sonos’s remote requirements and check the actual remote model and IR behavior before buying adapters or changing the audio system. Do not assume every Sony remote has the same IR capabilities.