GPU (Radeon RX 580) hardware decoding/encoding of H.264 and HEVC. Did this just begin working?

I recently converted 24 movies from HEVC to H.264 using latest Handbrake (~17min each vs. ~37min each via CPU only). I noticed some pixelated areas in one of the converted movies... but since then, I have played all the movies back under Windows, and they seem to be intact???

Does anyone know if the pixelated artefacts (well known from 10.14.4) are only visible if decoded using VideoToolbox under macOS??? or via GPU acceleration?

Not sure why MPV on Win10 seems to play all movies back perfectly?