SOLVED: Transcoding problem with LG WebOS

[Host-in-the-Shell]

I just want to point out for posterity, that the Intel Celeron J4125 is part of the Goldmont Plus microarchitecture, with codename Gemini Lake Refresh and it does support QSV. The reason you were having problems is because Synology DSM uses a custom build of Linux that tends to pack an ancient version of the kernel, which causes all these issues.

Anybody else using the same CPU with a more recent kernel should be fine.