@windg this, or just disable the "joystick control" part so you can still access the menu via an attached keyboard when needed, but players can't accidentally (or maliciously) do it with their gamepad.
@markyb2021 nope, i have 4 8BitDo Pads running very well and had no problems at all, not with retropie 2 x, nor with 3.x or 4.7.
It is your setup, but as you are not able to answer specific questions we will never know what is wrong with it.
@edward_ci that's how I understand it, yeah. As far as the emulator is concerned, it's just another USB gamepad. If the two gamepads have identical device names/IDs, then they'll use the same config file. So whatever mapping like button_12 = "A" or whatever is set in the config file, will be the same for both gamepads. If "button 12" is whatever button is wired in position "6F" on the board or whatever, and you have that wired to a different physical button, then your "A" button will be that different physical button. They need to be exactly the same.
@ts-x Great idea on dropping in on him. I might just do that. I have a wired number pad that I tried to use plugged into the USB port on my Mayflash (which would also avoid two long wires), but that didn't work. It's not a real USB port apparently. However, it would also be seen as another input device.
This issue is NUTS and across the whole retro industry. Someone needs to do something. Every joystick should come with the ability to ID itself as unique. If say, 8bitdo suddenly started offering controllers that all could send out unique IDs it would be a SHORT wait for someone in Retroarch and others to jump in and support that. That manufacturer would sell a ton of product and force everyone else to adopt that option as it would be SO brain-dead obvious. How has this NOT happened yet???