@zing Thanks !
Your link is a good ressource, it is specific to the exit button, so it's a good start. Also it worries me a bit: it shows that what I am trying to do is not that trivial.
Must mention in the discord someone suggested to connect my custom button to both existing buttons (hotkeys and start for instance to exit). It would work for sure, but I am not really fan of this solution as if a player is sending any input with his pad at the same moment, this will activate others hotkeys...
Thanks again for your link