Can my Apple TV remote be set-up to control the volume of my Bose Soundbar?

It appears this model soundbar originally has an IR remote. Then other IR remotes may emulate the same commands. Note that for volume control, the remote communicates directly with the audio system, not through the Apple TV. You will need unobstructed line-of-sight to the IR receptor on the audio system, same as with the original Bose remote.

If the default volume controls from the Apple TV remote don’t work for your audio system, then you may need to re-program for that device.

If you can't control your TV or receiver with your Apple TV Remote - Apple Support

For additional questions, please consult with Bose Support about support for third party remotes.

What is your model soundbar?

Does your soundbar have an IR receptor to receive such volume control commands from a remote?

Does your soundbar support volume control commands from any remote besides its own?