Well, due that NORMALLY, home theater are connected this way:
Sources -----> AVR ------> TV.
AVR extracts audio (your dolby atmos) and send them to speakers, so multi-channel audio doesn't even need to get to the TV. All TV cares is video.
So u say you don't have an AVR, but Soundbar supports atmos, well OK then same thing, buy a SB that does HDMI switching (multiple HDMI-IN in SB) so you can:
Sources -----> SB -----> TV.
P.S.: OK so you say you aren't going to use any external sources, you will watch whatever is available on TV's built-in Apps... in which case a TV with eARC, not a guarantee that atmos will be available to you, but at least it opens the possibility. TVs with eARC not widely available as of yet so you may have some waiting. U are hitting the breeding edge.