Format your USB drive
Step 1. List your disks and find your USB drive path
lsblk
Step 2. Clear all partitions and create a new one
(Take /dev/sdb as your USB drive path for example)
sudo fdisk /dev/sdb
Step 3. Umount your first partition
sudo umount /dev/sdb1
Step 4. Format your USB drive to FAT32
sudo mkfs.vfat -F 32 -n USB_name /dev/sdb1
Then, you can make your bootable USB drive with dd command. Good luck!