I've found the answer and solved the problem.I edited the file /usr/share/X11/xorg.conf.d/40-libinput.conf and I changed the following section (the one having pointer identifier), adding the two Option lines:
Hi everybody, I have a Latitude 5590 with Ubuntu 18.04 installed in dual-boot alongside Windows 10. Inside Windows 10, I can scroll pages by holding the central button and moving the trackpoint. Inside Ubuntu, such scrolling feature doesn't work. Any ideas? Thanks in advance.
Latitude 5590 - Ubuntu 18.04 - How to scroll with central button