adding the package xserver-xorg-input-libinput appears to have solved the problem. According to the folks at freedesktop, it should have defaulted to use the libinput driver, even without the 40-libinput.conf file, but in my case it didn't
** Changed in: xserver-xorg-input-libinput (Ubuntu) Status: New => Fix Released -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1967651 Title: Unicomp trackball/keyboard not recognised in Xorg sessions To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-libinput/+bug/1967651/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs