Picade supports a digital joystick, such as the one supplied in the Picade kit and available here: https://shop.pimoroni.com/products/zippyy-ball-handle-joystick
At the moment we don’t support analog joysticks since these aren’t common in retro arcade setups, but you could have a go at modifying the firmware to change this. It’s an Arduino-compatible board, so it’s very eminently hackable.
It also will not show up as a joystick, since out-of-the-box it’s designed to work with the Raspberry Pi and popular emulator software and is flashed with the original firmware we released to support the Picade kit.
The new 2.x firmware shows up as a gamepad, although with digital-only joysticks there’s no practical difference between this and keyboard mode, unless your particular emulator/game doesn’t support keyboard input: New 2.x Configurable Keyboard/Gamepad Firmware