Hi slikmik,
I have just gone through the same process as you for my M18.
grab the remote.conf from this post as it says its for your box: Ott mxq pro 4k s905 p201 remote.conf - FreakTab.com (found from google searching MXQ Pro remote.conf)
copy it to your device to this location: /system/.config ( after copying the file to the backup folder on the box using windows, i logged in using putty and used the cp command to move it to the .config folder)
using putty or something similar login in and run this: /usr/lib/libreelec/remote-config or reboot the system.if you fresh start another LE version just put the remote.conf in the root of the sd card before flashing and it should transfer across.
read these links if all your buttons arent working:
LibreELEC
LibreELEC
that config works on my box with the round m8 remote but no functions on my square remote that came with box, strange