@IG-88 To understand it fully, i asked him, if Hardware encoding works on his current system by using plex or emby and he wrote this:
"I do not know for sure. It definitely works for Video Station (using the Synology video license). My understanding that the Linux device /dev/dri needs to be present and functional for hw encoding to work in either Plex or Emby. I don't believe that the Synology video license has anything to do with that.
At one point in the past, I had a Xeon V5 (Skylake) with Quicksync and when I booted it on the 916+ image, /dev/dri was enabled.
My current usage of the 916+ image on the ASRock Apollo Lake/Gemini Lake chipsets, I do not see /dev/dri and have not investigated why since I do not need video hw acceleration. It's possible that the version of the dri driver baked into the 916+ DSM may not support the Apollo Lake/Gemini Lake CPU's for some reason. This might be something that can be addressed with extra.lzma if you ask IG-88, but you'll need to find a dri distribution that clearly offers support for the chip.
I didn't try this, but you might want to try the alpha 918+/DSM 6.2 install on your J5005 to see if /dev/dri is functioning on that platform. I don't really recommend it for production yet, but it might help you with planning."