This tab exists starting in WP Simple Pay 3.3.0. Prior to this, Stripe Checkout was the only display option.
On the Form Display Options tab, you can select the Embedded, Overlay, or Stripe Checkout display type.
Embedded will display all payment form fields on the page itself. All fields can be rearranged and styled as needed.
Overlay will display all payment form fields in an overlay launched by a button on the page. Like the embedded option, all fields can be rearranged and styled as needed.
Stripe Checkout will display some fields on the page and others in the Stripe Checkout overlay. Stripe Checkout is served up by Stripe’s servers and partial field customization. See Stripe Checkout Display Options to customize this further.
Form Title and Form Description are optional for Embedded and Overlay options.
If Stripe Checkout is selected, these fields are not available and you’ll instead want to set the Company Name and Item Description fields in the Stripe Checkout Display Options.