A:AnswerIf the fax machine is attached to the computer by way of a USB cable, you should be able to connect it in one USB port and connect the ds620 in another USB port.
A:AnswerMost Brother models like the Brother DS-620 offer support for macOS Catalina (macOS v10.15.x). Here is a link with additional information.
https://support.brother.com/g/s/id/os/macintosh.html