To create debian bootable disk you can use tools already available in macOS.
We are going to use:

• Disk Utility
• diskutil
• dd (/bin/dd)

1. With “Disk Utility” you can format usb memory, delete all partition etc. Select the external disk and format as FAT
2. Convert iso image to dmg, using the command:
   hdiutil convert debian-11.6.0-amd64-DVD-1.iso -format UDRW -o debian-11.6.0-amd64-DVD-1.dmg
3. Check external disk name
   diskutil list
4. Umount the disk
   diskutil unmountDisk /dev/disk4 // assuming /dev/disk4 is your external disk
5. Write the image to the external disk:
   sudo dd if=debian-11.6.0-amd64-DVD-1.dmg of=/dev/disk4 bs=1m

If you need to remove partition from your external drive and “Disk Utility” is no able to do that, you can use the following example: diskutil eraseDisk JHFS+ UntitledUFS disk4.
That would destroy everything what is on the drive and set the JHFS+ filesystem.

Note: there are other applications with nice GUI that can do the whole steps all together – but why not to use something that is already and ready to use.