A basic autoinstall.yaml I use for Ubuntu systems. This creates a base minimal server with a /boot, /, and /home (with /home taking up all the remaining space).

autoinstall.yaml

#cloud-config
# See the autoinstall documentation at:
# https://canonical-subiquity.readthedocs-hosted.com/en/latest/reference/autoinstall-reference.html
autoinstall:
  timezone: America/Chicago
  refresh-installer:
   update: true
  codecs:
    install: false
  drivers:
    install: false
  identity:
    realname: Your Name
    username: username
  kernel:
    package: linux-generic
  keyboard:
    layout: us
    toggle: null
    variant: ''
  locale: en_US.UTF-8
  interactive-sections:
    - identity
  oem:
    install: auto
  source:
    id: ubuntu-server-minimal
    search_drivers: false
  ssh:
    allow-pw: true
    authorized-keys:
    - '... your public key here, or you can remove this ...'
    install-server: true

  storage:
    config:
    - type: disk
      id: disk0
      ptable: gpt
      path: /dev/nvme0n1
      wipe: superblock-recursive
      preserve: false
      name: ''
    # Partition
    # /boot
    - type: partition
      id: partition-0
      device: disk0
      size: 1G
      flag: boot
      wipe: superblock
      number: 1
      grub_device: true
    # /boot/efi
    - type: partition
      id: partition-1
      device: disk0
      size: 1G
      wipe: superblock
      number: 2
    # /
    - type: partition
      id: partition-2
      device: disk0
      size: 50G
      wipe: superblock
      number: 3
    # /home
    - type: partition
      id: partition-3
      device: disk0
      size: -1
      wipe: superblock
      number: 4

    # Format
    - fstype: fat32
      volume: partition-0
      id: format-0
      type: format
    - fstype: ext4
      volume: partition-1
      id: format-1
      type: format
    - fstype: ext4
      volume: partition-2
      id: format-2
      type: format
    - fstype: ext4
      volume: partition-3
      id: format-3
      type: format

    # Mount
    - type: mount
      id: mount-0
      path: /boot/efi
      device: format-0
    - type: mount
      id: mount-1
      path: /boot
      device: format-1
    - type: mount
      id: mount-2
      path: /
      device: format-2
    - type: mount
      id: mount-3
      path: /home
      device: format-3

  updates: all # all | security
  version: 1
  shutdown: reboot # Or reboot | poweroff