Linux Kernel 5.9 is dead now as it is at the end of its life (EOL). According to Greg Kroah-Hartman, all the users using the 5.9 kernel series must upgrade. It is better to upgrade to Linux Kernel 5.10 LTS which was released a few days ago.
Linux Kernel 5.9 Reaches End of Life: How To Upgrade To Linux Kernel 5.10 LTS
You can download the Linux Kernel 5.10 LTS from the official website. You can also follow our blog on a tutorial to upgrade Linux Kernel in Ubuntu, CentOS, and other Linux based operating system.