Does new Mac mini M1 (2020) support Dolby Digital (5.1) audio?

I connected my Mac mini via HDMI to my Samsung Smart TV (using an HDMI 2.0 4k cable). The TV sends audio back to my Denon AVR via HDMI ARC. All works well, except when trying to play Dolby Digital (5.1) from my Mac mini (!?)

I noticed that when playing, for instance, Mythic Quest via the Apple TV+ app on my Smart TV, it sends Dolby Digital (5.1) signal to my AVR, but when playing Mythic Quest via the Mac mini app (or directly from Safari browser) it only sends PCM (stereo) to my AVR.

Does this mean the new Mac mini cannot support Dolby Digital or any 5.1 surround audio signals? Or is there something wrong in my setup?