I am an amateur, but I have installed the Retropie edition several times, without any problem with my joystick / IPAC2.
Being French, I said to myself, let's test a French product. Honestly, the RecalBox interface is really cool, but the simple configuration of a joystick kit on a Bartop with the IPAC2 usb interface is really a hassle.
I flashed my RecalBox several times on my SDCARD to be sure to leave on a fresh installation, and did many tests, without success. The behavior is as follows, I configure my joystick and its buttons without any problem in the RecalBox interface, I access all the menus.
But as soon as I launch a game (in this case those provided automatically, for example nintendo) the start or select button is not effective, and of course the hotkey does not work either.
I read all the forums, all the references to this famous link: https://github.com/recalbox/recalbox-os/wiki/Keyboard-encoder-configuration-(EN)
I am still blocked. It's a shame, the product looks nice, but if the recognition base of a joystick does not work hard to go further.