I can't answer you directly as I have no experience with Amiga hardware. But if I were you I would start searching if I can make the Amiga trackball compatible with USB HID protocol.
Which is not easy since, as far as I've seen in the pictures found around the internet, those mice used the serial interface.
There might be another option, but that would imply some research into available drivers: a USB to RS232 adapter.
Good luck and post back if you have some luck!
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