The Plex app on the TV will not passthrough TrueHD audio.
No TV supports TrueHD passthrough for TV apps.
According to rtings.com, the Sony will passthrough TrueHD + Atmos and dts-HD/:X audio via HDMI-eARC for devices connected to an HDMI input.
If you want TrueHD + Atmos audio you must use an external streaming device.
The Shield Pro will be your best option. It will passthrough TrueHD + Atmos and dts-HD / dts:X audio to equipment that support those formats. Do not purchase the non-Pro “tube” model. It has issues with high-bit rate media such as 4K HDR movies.
TrueHD passthrough was recently added to the Plex Xbox app. Additional information: Audio Passthrough support on Xbox beta . Others can fill in the blanks on how well this works. I’ve never used Plex on an Xbox and can’t speak to how well it does or doesn’t work.
Streaming devices from Apple, Roku, Amazon, etc do not support TrueHD passthrough. Some, such as Apple, convert it to lossless PCM, which is fine for TrueHD, but any Atmos info is lost. Others, such as Amazon FireTV devices, have no support, and TrueHD is transcoded to a lossy format such as AAC/AC3/EAC3, and Atmos info is lost in the process.
See this thread for additional details:
[INFO] Plex, 4k, transcoding, and you - aka the rules of 4k
