Found solution, but it took three days, because I'm no expert.
My system is Ubuntu 19.10.
Searching everywhere, I found that xorg intercepts all keyboard keystrokes (why?).
The problem is that mce remote is seen as a a keyboard, so also all his keystrokes are intercepted.
Don't know how, but all (real) keyboard keystrokes work, but not remote buttons.
Nobody has a wiki, a doc page that show how all this is managed by xorg/Ubuntu.
Anyway found that the solution was to exclude mce remote from devices recognized by xorg, and let the remote be managed by lirc.
So, at first, added my remote to the /usr/share/X11/xorg.conf.d/10-quirks.conf.
More precisely, as I found somewhere in a site, I added this to that file:
# Disable the MCE remote from acting like a keyboard. (We use lirc instead.)
Section "InputClass"
Identifier "MCE USB Keyboard mimic blacklist"
Driver "mceusb"
MatchProduct "Media Center Ed. eHome Infrared Remote Transceiver (1934:5168)"
Option "Ignore" "on"
EndSection
So, after a reboot, my mce remote was not seen by xorg.
Now I installed lirc.
Lirc package in Ubuntu 19.10 is defective.
When you first try to install, it terminates with an error because it doesn't find a file: /etc/lirc/lirc_options.conf.
So you have to copy (an empty text file is enough) a file with that name in that location, and install the package again.
After that, you have to edit lirc_options.conf and lircd.conf depending on your configuration.
I followed instructions on lirc site:
http://www.lirc.org/html/configuration-guide.html.
Reboot, and after lircd is started, all is working now!
I don't know other distributions, but kodi and mce remote is a really common hardware-software config.
How is it possible that a normal user has to do all that?
There's a complete lack of information.
I couldn't find anywhere how keystrokes are managed in ubuntu (or xorg).
Bye,
sdf