As Of: 26 Sept 2021
Use wget to get this installer script:
wget https://raw.githubusercontent.com/pimlie/ubuntu-mainline-kernel.sh/master/ubuntu-mainline-kernel.sh
Move this script to the correct directory:
sudo install ubuntu-mainline-kernel.sh /usr/local/bin
Run the installer to install the latest kernel.
sudo /usr/local/bin/ubuntu-mainline-kernel.sh -i