gnome-shell-extension-cyclop-updates

One icon in the panel that says whether this machine has updates waiting. It changes with the state of the machine: nothing waiting, updates waiting, or updates waiting of which some are security ones, which is a different sentence and deserves a different icon. Clicking it opens the Updates page of Cyclop Settings, where an update is explained and applied with a password prompt. It never installs anything itself and never runs apt. The count comes from apt-check, the same tool the rest of the system reports from, so two parts of the desktop cannot disagree about the same machine. It reads once at login, every half hour after that, and whenever apt changes its own files, which is what makes the icon correct the moment an update has been applied.

sudo apt install gnome-shell-extension-cyclop-updates