• The --network-veth option has been renamed to --netdev. The old name made sense with virtual ethernet devices, but when booting images with qemu a TUN/TAP device is used instead.
• The network config file installed by mkosi when the --netdev (previously --network-veth) option is used (formerly
  /etc/systemd/network/80-mkosi-network-veth.network in the image) now only matches network interfaces using the virtio_net driver. Please make sure you weren't relying on this file to configure any network interfaces other than the tun/tap virtio-net interface created by mkosi when booting the image in QEMU with the --netdev option. If you were relying on this config file
  to configure other interfaces, you'll have to re-create it with the correct match and a lower initial number in the filename to make sure systemd-networkd will keep configuring your interface, e.g. via the mkosi.skeleton or mkosi.extra trees or a mkosi.postinst script.
• The kernel-install script for building unified kernel images has been removed. From v13 onwards, on systems using kernel-install, mkosi won't automatically build new unified kernel images when a kernel is updated or installed. To keep the old behavior, you can install the kernel-install script manually via a skeleton tree; a copy can be found here.
• New QemuKvm option configures whether to use KVM when running mkosi qemu.
• mkosi will not default to the same OS release as the host system anymore when the host system uses the same distribution as the image that's being built. Instead, when no release is specified, mkosi will now always default to the default version embedded in mkosi itself.
• mkosi will now use the pacman keyring from the host when building Arch images. This means that users will, on top of installing archlinux-keyring, also have to run pacman-key --init and pacman-key --populate archlinux on
  the host system to be able to build Arch images. Also, unless the package manager is configured to do it automatically, the host keyring will have to be updated after archlinux-keyring updates by running pacman-key --populate archlinux and pacman-key --updatedb.
• Direct qemu linux boot is now supported with BootProtocols=linux. When enabled, the kernel image, initrd, and cmdline will be extracted from the image and passed to qemu by mkosi qemu to directly boot into the kernel image without a bootloader. This can be used to boot for example s390x images in qemu.
• The initrd will now always be rebuilt after the extra trees and build artifacts have been installed into the image.
• The github action has been migrated to Ubuntu Jammy. To migrate any jobs using the action, add runs-on: ubuntu-22.04 to the job config.
• All images are now configured by default with the C.UTF-8 locale.
• New --repository-directory option can be used to configure a directory with extra repository files to be used by the package manager when building an image. Note that this option is currently only supported for pacman and
  dnf-based distros.
• Option --skeleton-tree is now supported on Debian-based distros.