To use the iso, follow https://wiki.archlinux.org/index.php/USB_flash_installation_medium#Using_manual_formatting
wipefs --all /dev/sdb
mkfs.fat -F 32 /dev/sdb1
fatlabel /dev/sdb1 ARCH_202012
mount -o loop archlinux-2020.12.01-x86_64_openssh.iso /mnt/iso
mount /dev/sdb1 /mnt/usb
cp -a /mnt/iso/* /mnt/usb
sync
umount /mnt/iso
umount /mnt/usb