Even HEVC works depending on the client support; for example, I stream h.265/HEVC to my 4K TV and it decodes it just fine. (Which makes me wonder what formats the OP has things stored in that plex has to transcode, or what client device they're using)
Most anime releases are 10-bit h265/HEVC in Matroska container with ASS subtitles (which are a huge mess anyway and should stop being used), which isn’t supported anywhere at all.
