$ readlink -f /mnt/f
/mnt/f

but ls /mnt/f does not show the files in the root of the USB F:\ drive.

sudo mkdir -p /mnt/usb
sudo mount -t drvfs F: /mnt/usb
ls /mnt/usb

Backup C:\Sysgcc

sudo rsync -a --exclude='*.tmp' /mnt/c/SysGCC/ /mnt/usb/Backup2/SysGCC/