I got to work by using Apple TV 4K (2020) directly connected to Soundbar HDMI1 input and after Soundbar connected to Samsung TV by eARC HDMI.
Soundbar shows on display "Dolby Atmos" when Dolby content is playing.
Yeah, something with Atmos support in this app not working.
It works for me with app in Nvidia Shield connected to Soundbar and Hi-Res Audio gets more and more popular with a lot of Atmos releases. But for those without external media players it seems Samsung missed this one. Sad.
Atmos works in other apps like Disney+, HBO Max and Prime Video so I don't see why it wouldn't work in Tidal.