Debian 9: Install Newest Stable Kernel

[Linux for blind general discussion]

Samuel said:
Better yet, there is the backport of the 4.18.6 kernel which is
available precompiled. Instructions to use it are available on
https://backports.debian.org/Instructions/

I am running stretch (debian 9.6)
I attempted to follow the instructions linked above.
1. Add
deb http://ftp.debian.org/debian buster-backports main
to /etc/apt/sources.list
2. apt-get udpate
3. Got this message:
W: The repository 'http://ftp.debian.org/debian buster-backports Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ftp.debian.org/debian/dists/buster-backports/main/binary-amd64/Packages  404  Not Found [IP: 130.89.148.12 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.