Technically, mastering as we know it for a stereo song, doesn't apply for a file in Dolby Atmos format, that will be an ADM BWF file. Standart mastering means https://majormixing.com/dolby-atmos-mastering/ adding plugins to the master bus, but there is no master bus in a Dolby Atmos renderer, it simply can't exist there, since the resulting audio track in Dolby Atmos consists of greater than a hundred separate channels called audio objects. They are not united in one single master bus in the master track, they remain individual.