@Hyell Thanks for your effort, but it doesn't work.
The same happens:
The LCD works and shows everything, until the Retropie logo appears. After that and when emulationstation is loaded, the LCD keep working but now has a blinking cursor and ONLY shows messages from emulationstation (the game is on HDMI), like errors, various settings from emulationstation, legal info for MAME, etc.
If there is a setting to "tell" emulationstation to do the opposite, to start outputting the games on LCD this time and keep HDMI for messages only, it would be nice.