The low frame rate issue with IMX519 on Jetson Nano

Hello, I am using the iMX519 camera on Jetson Nano. The kernel version of Jetson Nano is Jetpack 4.6.2 (L4T 32.7.2). According to the specifications, 4K images (3840x2160) are supposed to have a frame rate of 21fps.

I ran the Jetson_IM519_Focus_Example-master that I obtained from GitHub. While I am getting 60fps at 720p and 120fps at 1080p, the frame rate for 4656x3496 and 3840x2160 is only half. Does anyone know why this is happening?