Update 2020-05-07: This also works with Lubuntu 20.04 LTS Focal Fossa.
I’ve searched the internet looking for a way to enable tap-to-click on Synaptics touchpads in Lubuntu 19.10 Eoan Ermine and have tried the .conf file variants those searches throw up. None of these has worked for me.
It turns out enabling tap-to-click is much more straightforward than the internet would suggest. To enable tap-to-click, open QTerminal (or the terminal of your choice) and enter the following command:
sudo apt install xserver-xorg-input-synaptics
Enter your administrator password and, once the package has finished installing, reboot your computer. Tap-to-click should now be enabled.