So just in case this is helpful I have an x13 but when I was installing any version (tried a few) I had to use a single-band network (5ghz only in this case, had it for other reasons already) because the installer would just never report it was connected to the network even though it was, I had assumed it was that my multi-band network also included 6ghz. Either way though, this seemed to be only an issue for the installer and when it booted up after install I could use the multi-band network just fine. It currently has 24.04 on it and it is fine.

I had a few ideas, I’m suspicious that handbrake is falling back to CPU, maybe check the logs of the container to make sure it isn’t falling back to CPU decoding. Otherwise here are a few things I would check next:

• If you are not using docker locally so you are already doing this, you will need to configure the docker container to pass through the GPU for quicksync to work inside the container.
• If you are already doing that then I would make sure the device is the same name on the synology, it probably is but just to be sure.
• you will likely need to add your user to the video and/or render group on the synology if you haven’t, especially if you are running the container as your user instead of root
• make sure you are reading and writing to volumes that use bind mounts and not docker volumes, overlayfs is not what I would call fast and writing especially.