I have installed every ubuntu package downloaded by the SDK manager,but my jetpack 4.4 has not been upgraded to 4.5.1

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
9

I feel unsure for your case, so take my advice with caution…

Seems the problem is with xusb firmware and initrd.
What I would try in this case would be adding update-initramfs hook such as here (step 2).