Khadas MIPI Camera does not work properly

I am using Khadas MIPI camera module (OS08A10) with Ubuntu Focal.
I can`t retrieve frames at the propper framerate. As I see in the khadas linux sources this camera should support 1920x1080 60fps mode. But it always works with 17-20 FPS.

I use OpenCV VideoCapture to get frames. When I set CAP_PROP_FRAME_WIDTH to 1920 and CAP_PROP_FRAME_HEIGHT to 1080 the frames comes with framerate around 17-20 fps. And I see abnormal CPU usage while capturing (100% usage on one of the cores).
If I don`t set CAP_PROP_FRAME_WIDTH and CAP_PROP_FRAME_HEIGHT then the frames comes at a framerate ariund 35 fps and image format is grayscale (1-channel) 3840x2160.

I also tried using gstreamer to capture the camera. But it works with the same framerate 17-20 fps.

How can I use the camera with the declared framerate (at least 30 fps) ?
Can I get documentation about Amlogic camera/isp sub-system so I could try to find the issue ?