2019-10-02, 22:15
I received confirmation on the CoreELEC forum in the meantime: HDR is known not to work in the VP9 codec chain. They do not know why, but reckon that it's either in the kernel or in an amlogic blob. If it is a kernel problem it might get fixed in the future, otherwise it is up to amlogic and nobody knows. At least I know that I didn't screw up my settings. Will watch the space and report back here if things should change...