• The default kernel command line of console=ttyS0 (or equivalent for
  other architectures) has been removed. The required console=
  argument to have the kernel output to the serial console has to be
  added manually from v24 onwards.
• Support for installing local packages located in directories in
  BuildSources= was dropped. Instead, the packages can be made
  available for installation via PackageManagerTrees=.
• Configuration parsing was reworked to remove the need for the @
  specifier and to streamline building multiple images with
  mkosi.images/. If you were building multiple images with
  mkosi.images/, you'll need to adapt your configuration to the
  rework. Read the Building multiple images section in the
  documentation for more information.
• mkosi has gained the option to generate completion scripts for bash,
  fish and zsh. Packagers should generate the scripts during packaging
  and ship them in the appropriate places.
• Added support for CentOS Stream 10.
• mkosi now installs a separate mkosi-initrd script that can be used
  to build initramfs images intended for use on the local system.
• We do not automatically append centos-stream or fedora anymore to
  CentOS (and derivatives) and Fedora mirrors specified with Mirror=
  as not all mirrors store the repository metadata under these
  subdirectories. Users are now required to add these subdirectories
  themselves in Mirror=. If the EPEL repositories are enabled for
  CentOS Stream (and derivatives) and Mirror= is used, we look for the
  EPEL repositories in ../fedora relative to the mirror specified in
  Mirror=.
• We now support compressed tar archives wherever we already accept tar
  archives as input.
• We now always rerun the build if Format=none and don't remove
  previous outputs in that case (unless --force is specified). This
  allows using mkosi -t none to rerun the build scripts without
  removing the previous image. This can then be combined with
  RuntimeBuildSources=yes to make the build script outputs available
  in a booted container or virtual machine so they can be installed
  without having to rebuild the image.
• We now use virtconsole to provide the serial console when booting
  with qemu.
• root=PARTUUID and mount.usr=PARTUUID on the kernel command line
  are now automatically extended with the actual PARTUUID of the
  corresponding partition.
• All available OpenSUSE repositories are now supported and can be
  enabled with Repositories=.
• Building OpenSUSE aarch64 images is now supported
• mkosi dependencies was beefed up to handle more scenarios properly
• The default list of kernel modules that are always added to the
  initramfs was extended with various virtualization modules.
• Added a Repositories= match.
• Cached images are now invalidated if packages specified via
  PackageDirectories= change.
• Added VolatilePackageDirectories= which can be used to provide local
  packages that do not invalidate cached images.
• mkosi.pkgmngr is now used as the default path for
  PackageManagerTrees=.
• The package directory that build scripts can use to make built
  packages available for installation ($PACKAGEDIR) is now shared
  between all image builds. This means that packages built in earlier
  images and stored in $PACKAGEDIR become available for installation
  in all subsequent image builds.
• The default tools tree distribution is now chosen based on the host
  distribution instead of the target distribution.
• mkosi can now be invoked from the initramfs.