I’ve recently installed Lubuntu 19.10 and got everything almost fully working, however I’m currently having to use autologin because the login screen doesn’t display any virtual keyboard and I’m on a tablet.
I have onboard installed, and I have also tried to install qtvirtualkeyboard (via apt-get install qtvirtualkeyboard*) and editing the sddm.conf file, however all I managed to do was get the screen to go black with no virtual keyboard appearing.
I have used KDE and SDDM and know that on the tablet the black screen part is normal, but usually accompanied with the keyboard appearing over the black screen so I wondered if I’ve missed an option etc.
I’m a new Lubuntu user for a couple of days. I get SDDM flickers and need to install a different theme compatible with my old hw. I have seen some desktop lacks, instead it’s a vibrant project and I enjoy it. I am on Lubuntu 20.04 beta and I have the same problem as you. I don’t use virtual kbd but I found the following:
$ grep -i virtualkeyboard /var/log/* | tail -10
/var/log/syslog:Mar 23 11:03:00 icetwr sddm-greeter: qrc:/QtQuick/VirtualKeyboard/content/InputPanel.qml:125:5: Type Keyboard unavailable
/var/log/syslog:Mar 23 11:03:00 icetwr sddm-greeter: qrc:/QtQuick/VirtualKeyboard/content/components/Keyboard.qml:37:1: module "Qt.labs.folderlistmodel" is not installed
qml-module-qtquick* is installed, not so qml-module-qt-labs-folderlistmodel and should be.
Then you’ll find a drag button on the login screen to show the keyboard.