Sorry, can't really comment on RF remotes, maybe someone else has a recommendation.
If you have an IR receiver on your RPi configure your Harmony to the Microsoft Media Center profile - this will work out of the box with LibreELEC.
CEC may be another option.
I'm mainly using an IR remote on my RPi, sometimes just CEC for basic navigation and if I need to enter lots of text I have a Logitech K400.
so long,
Hias