ah, and it only works with GPU acceleration enabled
Thank you, switching to rocm and gpu accel solved this issue (though my Polaris struggles a bit compared to CPU, possibly due to the scaling shaders already running on it). Perhaps it should be added to the 4k/hdr wiki page that 10 bit output only works with gpu acceleration enabled.
This thread can be closed :+1:
Edit: my performance issues were only from the separate chroma upscale shader I was using in combination with FSRCNNX. Disabled the chroma upscale shader, and getting solid performance no matter svp settings!