How can I modify it to use the middle click?

[Pedro Galvão]

The middle mouse button still works, minus the scroll, so I would like to emulate using it instead of the right button.

[Kris]

Just remove the line libinput_device_config_scroll_set_button(device, 273);. It'll set default value which is middle button.

[Pedro Galvão]

Thanks, that worked!