The linked article is about the use of HomePods or HomePod Minis for when the content source is not the Apple TV box. It doesn’t apply to soundbars. It doesn’t apply to content streaming from apps on the Apple TV box.
Functionality and connections may differ for various models soundbar. Please specify your model.
Often a good setup is to connect as
Apple TV →[HDMI]→ TV →[HDMI ARC/eARC]→ soundbar (ARC: stereo or DD 5.1; eARC: any audio format)
or
Apple TV →[HDMI]→ TV →[optical/coax/RCA]→ soundbar (optical/coax: stereo or Dolby Digital 5.1; RCA: stereo)
and set the TV for audio passthrough to the soundbar for all content.
Without a high bandwidth connection to the soundbar (eARC or direct), PCM Multichannel or Dolby Atmos (Dolby MAT) is not supported/available. Then set Apple TV audio format to output in Dolby Digital 5.1 or Stereo. Adjust other audio settings on Apple TV - Apple TV user guide - Apple Support