entity_reference.schema.yml

field.entity_reference.instance_settings:
  type: mapping
  label: 'Entity reference settings'
  mapping:
    handler:
      type: string
      label: 'Reference method'
    handler_settings:
      type: entity_reference.[%parent.handler].handler_settings
      label: 'Reference method settings'
      
entity_reference.default.handler_settings:
  type: mapping
  label: 'View handler settings'
  mapping:
    target_bundles:
      type: sequence
      label: 'types'
      sequence:
        - type: string
          label: 'Type'
    sort:
      type: mapping
      label: 'Sort settings'
      mapping:
        field:
          type: string
          label: 'Sort by'
        direction:
          type: string
          label: 'Sort direction'


# From views/config/schema/views.entity_refence.schema.yml


# Schema for the views entity reference selection plugins.

entity_reference.views.handler_settings:
  type: mapping
  label: 'View handler settings'
  mapping:
    view:
      type: mapping
      label: 'View used to select the entities'
      mapping:
        view_name:
          type: string
          label: 'View name'
        display_name:
          type: string
          label: 'Display name'
        arguments:
          type: sequence
          label: 'View arguments'
          sequence:
            - type: string
              label: 'Argument'