I searched for the last download that I used in 18.04. Please see -
which is in Italian and which I don't pretend to understand. However, I clicked on the download link within the page which led me to -
where I chose to use the direct download rather than Save to my dropbox. I was then prompted by a dialog box to either save or open with Engrampa.
I saved (to my downloads folder). I also tested the dropbox download which worked. From there you can install and use Systemback within Ubuntu-MATE 18.04.
I booted into my install of 18.04 and looked at systemback using Synaptic. This is what I found:
I personally haven't used Systemback since 18.04 replacing it with Clonezilla which I use from Parted Magic. For details on that, please see -
https://ubuntu-mate.community/t/boot-a-live-cd-iso-on-your-hard-drive-using-grub2/
For the curious, see the following pages found when chasing down the Italian page:
https://www.linuxbabe.com/ubuntu/install-systemback-ubuntu-18-04-bionic-18-10 where the author presumably downloads and installs systemback. I didn't test these instructions for accuracy or reliability.
https://gitlab.com/Kendek/systemback/ where supposedly systemback is still undergoing development. Also not tested for any sort of reliability.
Good luck computerguy.