The USB cable is only "rather pointless" without the needed software: Motorola Software Update (MSU) and P2kCommander (P2kC) - both free downloads ... Google for them. Not sure whether your
PEBL can use the latest version of P2kC; my Moto Z6tv can, but my wife's uses an earlier version (4.9.E). After you plug in the USB cable, you launch MSU, and then P2kC. It is P2kC that will allow you to access the phone's file system and copy your files from the phone to your computer.