I saw this man page:

https://www.mankier.com/4/libinput

But where is the file I am supposed to configure? I would like to emulate the middle button. I would like to be able to use my trackball to scroll with a middle button push. xinput says I am using wayland. I suspect xinput must be an obsolete command?

I looked under /etc/X11, but the only file ending in .conf is my file xrdp.conf.

This is from sudo libinput list-devices. The doc says the libinput command cannot be used to change current settings.

Code:
Device:           Kensington USB OrbitKernel:           /dev/input/event2
Group:            5
Seat:             seat0, default
Capabilities:     pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: disabled
Calibration:      n/a
Scroll methods:   *button
Click methods:    none
Disable-w-typing: n/a
Accel profiles:   flat *adaptive
Rotation:         n/a