linux-headers-5.4.0-56 generic
The simplest method is to remove the problematic package by
sudo apt-get purge linux-headers-5.4.0-56-generic
or in low-level
sudo dpkg -P --force-all linux-headers-5.4.0-56-generic
Then install normal latest kernel and its headers using:
sudo apt-get update
sudo apt-get install linux-headers-generic linux-image-generic
sudo apt-get install --reinstall linux-headers-$(uname -r)
sudo apt-get install --reinstall linux-image-$(uname -r)