Why aren't my states showing in the Default field when setting up Order Items Type State Workflow for order fulfillment?

Question

I'm following the instructions to set up Order Fulfillment States as per Working with state fields but when I attempt to add a new State Field the states specified in my module.workflows.yml aren't showing up as options to set the Default state. I'm not getting any errors, and I ran my yml through ChatGPT to check it.

Here's my yaml.

  id:  teflfill_order_item_fulfillment
  group: teflfill_order_item
  label: 'Order item fulfillment'
  states:
    unfilled:
      label: 'Not filled'
    filled:
      label: Filled
    backordered:
      label: Backordered
  transitions:
    fill:
      label: 'Fill item'
      from: [unfilled, backordered]
      to: filled
    unfill:
      label: 'Un-fill item'
      from: [filled]
      to:   unfilled
    backorder:
      label: 'Backorder item'
      from: [unfilled]
      to: backordered