Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
Tubi doesn't seem to have multi channel audio capability. Anything that I view on that app delivers downmixed stereo audio. No matter the movie (that I know has 5.1 audio) there is no multichannel sound at all.
It's just Tubi, the Roku channel supplies multi channel to the majority of its listings.