This is a popular topic - Connecting Bluetooth Headphones to a SmartTV that is connected to a SONOS Soundbar using HDMI-CEC (Beam, ARC, PlayBar ...). I have Sony WH-1000XM3 headphones. What works for me is to connect the TV (Samsung SmartTV) to a Bluetooth transmitter using an optical cable. The analog output (audio jack) from the Samsung TV is not active when the TV is connected to the Beam over HDMI-CEC, however, there is a signal on the optical interface. This configuration supports simultaneous audio over the headphones and soundbar. You will need a Bluetooth transmitter that supports an optical input. After turning on the headphones and successfully pairing with the Bluetooth transmitter, I double tap the right headphone (Sony’s touch sensor control) to “play” the TV’s audio over the Bluetooth transmitter.