in order to get big sur to recognize your USB drive & show it on the desktop Open Disk Utility Choose "Show All Devices" from the View menu Select the destination drive hardware (above the existing volume) Click Erase Choose the "GUID" partition scheme (2nd pop-up), THEN "APFS" formatting (1st pop-up) and name appropriately Click Erase if you have files on the USB drive you should be able to open them with an app & then save them, if they are essential, before you erase.