Well, I've now a general procedure to get Recalbox running on a Pimoroni Picade.
Because I think this could be a valueable information, I decided to finish this thread and to open a new and fresh one. So nobody has to read through all the posts in this thread to come to the solution.

@rk-aus-s

Ich kenne mich damit leider nicht gut aus.
Falls du noch einen Controller hast, verbinde ihn.
Und versuche damit "ok" auszulösen.
Oder mit dem Smartphone z.B. (http://recalbox oder http://recalbox.local)
Dort kann du den virtuellen Controller nutzen.

@kooper
Illegal stuff.

@sziszee it's recalbox, not retropie, you must configure your joysticks in EmulationStation, not retroarch

@aarenj

Have you tried this ?

https://forum.recalbox.com/topic/13906/update-18-04-2018-x86-x86_64-sound-problem

@Substring je comprend totalement.
La partie matériel est prévu, je vais en fabriquer une autre plus grande avec un teensy.

Je vais quand même chercher une astuce ou deux pour jouer sur cette game boy.

Pour la partie codage, je vais pas te mentir, ça ne m'a jamais vraiment attiré mais si je n'ai pas le choix, je m'y pencherais.

Merci en tout cas pour ton aide, si je trouve des truc, je les mettrais ici.

@dragu if you were looking for a CM3 project, here is one !

@stresstester hmmm if I remember well, Doom should run well on dosbox, maybe you have to tweak the con fil

@abunille Going to try this later today hopefully! Thank you so much.

For me keyboard was working well until i did upgrade to the latest updates that stoped working...

@andre-wollny

here you find the commodore 64 keyboard map
https://www.flickr.com/photos/63158896@N08/6176425740/

here the emulator keymap
https://github.com/libretro/RetroArch/blob/master/input/input_keymaps.c

For example the RUN / STOP key is mapped to ESC (RETROK_ESCAPE)

Press Hotkey + B to configure
QuickMenu->option to joypad key setup
QuickMenu->option->create game-option file to save

@andré-alcover-rodrigues so you have a SEMICO USB keyboard. It has 2 possible events. You should start evtest and test bith to see which one is responding when you're typing on it. Write down its name, and find to which /dev/input/by-id it corresponds to

Next, in the moonlight.conf, simply add that /dev/inout/by-id/blablabla that worked

Hello @cumberfan221b

keyboard only Emulationstation : https://github.com/recalbox/recalbox-os/wiki/Manual-(EN)#keyboardmapping
you need a bluetooth gamepad or usb gamepad to play game.
https://www.youtube.com/watch?v=xxlRoFHg4vs&list=PL2oNQ0AT7fx2ExiSNrfHUzga5GnogI4sh&index=3
enable english substitles

Hey never mind, just came back to delete my post. I just flashed the card and booted it up. Running smoothly now, better than I could imagine. Thank you for offering help.

My bad... The config of my keyboard had just nothing to do with everything I could find on the web... It actually works.

Je sais pas si ça peut aider mais en suivant ça : http://www.correlatedcontent.com/blog/bluetooth-keyboard-on-the-raspberry-pi/
J'ai mon clavier qui était fonctionnel (genre pour saisir un ssid).

I checked the default controls and I can go back to the menu using "hotkey+start" in my DS3 pad.

I can do all I need with my DS3 pad.

Thanks for your support.