Lubuntu 21.04: forcing natural scrolling on a mouse

I like natural scrolling — the inverse of how most Linux systems configure a mouse. If I want to scroll upwards, I pull down on the mouse. And vice versa.

There is a GUI for this in Lubuntu but, for whatever reason, my settings did not persist across login sessions. Which is a pain.

The answer which worked for me was:

vim /usr/share/X11/xorg.conf.d/40-libinput.conf

And adding to the Input Class Identifier "libinput pointer catchall":

Option "NaturalScrolling" "on"

This forces it on for all pointers (trackpad, mice etc.), but I could not find a way of setting it separately for the mouse.