layout_builder.layouts.yml

layout_twocol_section:
  label: 'Two column'
  path: layouts/twocol_section
  template: layout--twocol-section
  library: layout_builder/twocol_section
  class: '\Drupal\layout_builder\Plugin\Layout\TwoColumnLayout'
  category: 'Columns: 2'
  default_region: first
  icon_map:
    - [first, second]
  regions:
    first:
      label: First
    second:
      label: Second

layout_threecol_section:
  label: 'Three column'
  path: layouts/threecol_section
  template: layout--threecol-section
  library: layout_builder/threecol_section
  class: '\Drupal\layout_builder\Plugin\Layout\ThreeColumnLayout'
  category: 'Columns: 3'
  default_region: second
  icon_map:
    - [first, second, third]
  regions:
    first:
      label: First
    second:
      label: Second
    third:
      label: Third

layout_fourcol_section:
  label: 'Four column'
  path: layouts/fourcol_section
  template: layout--fourcol-section
  library: layout_builder/fourcol_section
  category: 'Columns: 4'
  default_region: first
  icon_map:
    - [first, second, third, fourth]
  regions:
    first:
      label: First
    second:
      label: Second
    third:
      label: Third
    fourth:
      label: Fourth