It was an accessory to let you use Amiga joysticks on the PC, from the mid 90s. I had one.

Could well have been, though I’m still picturing a computer in my mind. Wasn’t the SAM Coupe, but that’s the sort of thing I’m recalling.

But: it was probably quite common on joystick interfaces, now you mention it. Thinking along those lines and searching for ‘twin joystick adapter’ let me actually find an example: https://www.ebay.com/itm/276075015721

Worth noting that in the image that shows two joysticks plugged in they really don’t look like they fit all that well…