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.

Changed engine core to pcsx_rearmed and it's fixed!

@aintmichael
There is still one option staying, to replace the dosbox version in the packages with an older one, working pretty well for me and that I use currently. As /usr/bin/dosbox
Older Dosbox version

reinstalled RecalBox without resizing and let the Pi and the system took care of it. Now there is a third "shared" Patition and everything saves persistently. Thanks for help. This issue is solved :)

I solved used Sixasis Pairing tool from Windows, i forced my "problematic" Shanwan to connect to Raspberry BT address.
Now i have the problem that all 2 shanwan copies are detected as "Playstation 3 original" , but i selected Shanwan drivers from configuration and i read that supports "original and shanwan" , so at the moment i cannot see any issue with this.

Recalbox is free and support is not expected to be given quickly, i just ask if somebody can shed light about where BT pairing informations are stored, why Shanwan copies are detected as Ps3 original and so on.

In the FAQ, in the tutorial we can add Sixasis Pairing tool way for problematic controller, i can give my availability to improve the community experience.

I also had other issues with Ps3 ORIGINAL pad (that now i use only with Android phone), this device often pressed buttons, never really pressed! Led often stay OFF, but pad was working (with ghost pressing issue).
I thought was a problem with pad, but with Android works like a charm, maybe if reoccurs with Shanwan units i should open another thread.

@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

@xnet1986 you're welcome!

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

@samzdrone with ps4 joystick that´s OK ? You used what version ?
If update to new version crash you need to reinstall recalbox :(

@kabukibear

done
next time you can mark it also yourself :)
Topic Tools -> Ask a question + Topic Tools -> Mark as Solved

@joseph-portuondo It seems to me you are using batocera and not recalbox

Ok. I made it work now completely (including start and select buttons) by setting global.inputdriver=sdl2 in the config. Thus, this thread can be closed.

@gavsta depending on the romset you use, you put your roms in different folders. On different folders, the cores are also different. You must specify exactly which romset you are using and in what folder you are putting the rom, plus any relevant modification you might have done. Wirh incomplete info we can't help. Read the arcade wiki if you don't know what I'm talking about.

Allright, thanks for the replies! Gamepad is already shipped, but it's gonna take a few days (coming from Japan) =)

dunno about straight/crossover cables, but it does require DHCP