Standard is a normal catering/event quote (pickup, delivery, on-site, invoicing or venue) with a Banquet Event Order. Personal Chef is a household meal plan: the fulfillment type is fixed to On Site, start/end times are not required, and instead of a BEO you get a Weekly Menu tab where each meal is assigned to a day of the week and (optionally) to a specific household member.

Which types you can create is controlled in Client Config under the Order: Catering tab by Proposals: Allowed Proposal Types (Both Standard and Personal Chef, Standard only, Personal Chef only). When only one type is allowed the type picker is skipped and "Add New From Scratch" goes straight to that type. The type is chosen at creation and cannot be changed afterwards.