[vaylian]

How does the update process work? Do you run pacman -Syu and then bake the result into the next image with mkiso?

[DaanDeMeyer]

mkosi runs pacman for you and then packs up the result as a disk image. It also builds a unified kernel image and does a bunch of signing. The new /usr partition and UKI are then installed with systemd-sysupdate.