To use the cheapo USB touchpad branded as Jelly Comb WGJP-012 on Debian 10 Buster, you might have to do a bit of tweaking.
Make sure you have
Make sure you do not have
Create a file
/etc/X11/xorg.conf.d/40-libinput.confwith the following contents.
Section "InputClass" Identifier "libinput touchpad catchall" MatchIsTouchpad "on" MatchDevicePath "/dev/input/event*" Driver "libinput" Option "Tapping" "on" EndSection
After a reboot, you should be able to left-click (single tap), right-click (tap with two fingers) and scroll (swipe with two fingers.)
(Infos taken from the Debian Wiki, but shortened for the Jelly Comb touchpad.)