The package has a debian/watch file, but the last attempt
to use it for checking for newer upstream versions failed with
an error:
In debian/watch no matching files for watch line https://github.com/paradoxxxzero/gnome-shell-system-monitor-applet/releases .*?(\d\S*)\.tar\.gz
testing migration
This package will soon be part of the gnome-shell-45 transition. You might want to ensure that your package is ready for it.
You can probably find supplementary information in the
debian-release
archives or in the corresponding
release.debian.org
bug.