ostree-boot 2020.3-1 (s390x binary) in ubuntu focal

 libostree provides a library and tools for managing bootable, immutable,
 versioned filesystem trees. See the ostree package's description for
 more details.
 .
 This package contains configuration snippets and executables needed to
 boot a Debian derivative from a libostree filesystem deployment. This
 integration currently has some limitations:
 .
  - the initramfs must have been made using dracut
  - /boot must be a separate partition
  - the boot loader must be one that is supported by libostree, currently
    GNU GRUB 2, syslinux/extlinux or Das U-Boot