@Djoss, @Taddeusz, thanks a lot for commenting.
Djoss, I did all those you mention, and couldn´t start the container with the dri device as it was not existing. Tried several times, started the array, booted the pc etc.
BUT, "something has happened overnight", the dri device (or directory) is now existing and I can add the device now.
And.. Handbrake has now the Intel QSV option, which was the target
So, I´m off to testing the thing. Kudos to you both, greetings from Finland