System tray icons not showing up in Mate panel (Ubuntu 18.04)

Last week I upgraded Ubuntu on my desktop computer from 16.04 to 18.04, and I found out that the system was gone. I tried to add it, with no success. It’s annoying that the applet name is not something suggestive, like “Application Tray”, or “System Tray”, I had always struggled when I had to re-add it in the past, both in Gnome and in Mate.

So, I studied all the items in the available applets in order to find the needed one, but it was missing. Then I did a search and found this thread.

Long story short, the solution was to install mate-tweak:

sudo apt install mate-tweak

Then right click on the panel > Add to panel:

Next, find the applet named “Indicator Applet Complete”, and drag it to the panel, wherever you want it to be.

Now you have it:

But hey, “Indicator Applet Complete”? That’s a very suggestive name for the system tray.