backports-5.5.11-1 was released. This is based on Linux 5.5.11.
https://cdn.kernel.org/pub/linux/kernel/projects/backports/stable/v5.5.11/backports-5.5.11-1.tar.xz

backports-5.4.27-1 was released. This is based on Linux 5.4.27.
https://cdn.kernel.org/pub/linux/kernel/projects/backports/stable/v5.4.27/backports-5.4.27-1.tar.xz

backports-4.19.112-1 was released. This is based on Linux 4.19.112.
https://cdn.kernel.org/pub/linux/kernel/projects/backports/stable/v4.19.112/backports-4.19.112-1.tar.xz

There is now a updated wiki page with the releases:
https://backports.wiki.kernel.org/index.php/Releases

The source code can be found here:
https://git.kernel.org/cgit/linux/kernel/git/backports/backports.git/

Hauke