Although Apple didn’t really officially announce this but some developers claimed it is and if so, then Plex and InFuse app can finally support bitstream of lossless audio like Dolby TrueHD, DTSHD MSTR/DTS:X MSTR and possibly Dolby Atmos as well. There is possibility that Apple only support Dolby Atmos up to DD+ with (JOC) capability akin to most streaming platforms like Apple TV+, Netflix, Disney Plus. We shall find out soon.
Source: Apple TV 4K Set To Support HDMI Audio Passthrough In TvOS 26
Apple TV 4K has always been unique in that it has always supported lossless audio. In fact, the Atmos you get on the Apple TV 4K is lossless LPCM + Atmos metadata (Dolby MAT).
The problem is that the streaming services (Even Apple TV+) send Atmos with a Dolby Digital+ encoding. Hence, the Apple TV 4K has to recode the lossy DD+ signal into lossless LPCM+Mat. The ATV4K has far more processing power than the streaming services are able to provide.
I think the issue with Plex and other apps is that they cannot communicate with the Apple API to convert TrueHD and DTS MA into Apple’s LPCM + Mat format. Hence if the new TV OS allows bitstream to go through, the apps can play lossless audio directly. Hopefully then, Tidal can also stream losseless Atmos music as they are using DD+ now.