headset connected with optical cable

Do you have another headset connected with an optical cable perhaps?

If you have tried that but still can't enable Dolby Atmos while you have everything plugged in, then just disconnect the optical cable but leave the USB plugged in, which is what charges the headset, not the optical cable.

The optical cable does not trigger the Xbox to see the base station...it's the USB cable that - when connected - prompts the Xbox to recognize the presence of the base station/headset and disables Atmos. So it's not possible to charge the headset and use
Atmos.

The optical cable can stay plugged in at all times and does not effect the ability to enable Atmos.

what connection are you using for the TB headset? If it's also an optical cable, try switching that out. optical cables are quite fragile and a crack in the plastic could cause you to lose sound.

All the info for the headset's and uses are here. It should have your answer.

https://beta.support.xbox.com/help/hardware-network/accessories/connect-compatible-headset

The audio adapter plugs into the large AV socket above the HDMI socket on the back of the console. The green-red/white audio cable that came with the headset then connects the headset to the adapter.

This then gives a direct audio signal from the console to the headset.

If you are the owner of an original Xbox 360 (large) and have purchased a headset that connects to the console via an optical cable, you will need to purchase the HDAV Adaptor(unless already supplied with your console at purchase). The HDAV Adaptor connects
to the rear of the console and gives you the optical port not included on the console. (The slim Xbox 360 has an optical port as standard)

If using HDMI to connect to the TV you will need to purchase the HDAV Adaptor to use the headset. The AV port on the console is very close to the HDMI port, this means that when a HDMI lead is connected to the console the standard AV lead will not fit.

The HDAV Adaptor has been made to allow both itself and the HDMI cable to be connected at

the same time.

If your headset is a stereo headset (not connected via optical) and your TV does not have Red and White stereo audio phone's out. The HDAV adaptor is equipped with Red & White stereo audio out phones as well as an optical port so your stereo headset connects
here.

It should also be noted that if a HDMI cable is not being used, i.e. a Component cable or composite cable is used, then wired headsets can piggy back with those connections so the HDAV adaptor is not needed.