As explained in our support articles on hardware transcoding, support is not yet available for the AMD GPU platform. Some limited functionality may work, but it’s on an as-is basis, without any guarantees from Plex. We do plan to add full support for the platform, but there’s a fairly large amount of work required to do so, as it uses entirely different APIs on Windows for video postprocessing than the ones we use on Intel (or on Nvidia for that matter), so without a lot of new code, the available performance is severely limited. There’s work in progress in the upstream ffmpeg codebase to add the necessary infrastructure for high-performance transcoding on AMD GPUs on Windows, but it’s not yet complete.
