To be honest, I don’t even know if this is even a supported configuration, but I was happy that with Infuse5 Pro, I could finally get properly tone mapped 4K HEVC coded UHD content show properly on my ATV4 (not 4K!).
However, now my content stutters like there is no tomorrow, whereas the Plex tvOS app would x-code on the server and then playback smoothly on the ATV4.
So, now, I am in a quandary … (1) watch content with washed out colors, but have smooth playback ATV4 → Plex tvOS app, OR (2) get properly tone mapped colors, but suffer stuttering video.
Correct, in order to play 4K HEVC videos without transcoding you will need the newer Apple TV 4K model.
The transcoding features coming in the upcoming version of Infuse should allow you to watch these videos with proper tone mapping, but of course you will be losing a bit of quality due to the transcoding process.