Currently Infuse doesn’t (get to) support audio format of Dolby TrueHD with Dolby Atmos on Apple TV 4K boxes (similar to many Blu-ray discs with Atmos tracks). Dolby TrueHD with Dolby Atmos will be output as PCM Multichannel 7.1 without Atmos instead.
Infuse supports Dolby Atmos when using E-AC3 audio tracks (Dolby Digital 5.1 or 7.1 with Dolby Atmos) (same as streaming providers).
Unfortunately this app (nor any other app) isn’t able to convert the former to the latter on-the-fly. Either format is a export from the master source using Dolby software.
Audio options (tvOS) - FireCore Infuse Support