Where did the one-line options format go in the item form?

It was replaced by ordinary fields. Open Edit on an item, look under 'Choices and extras', and press '+ Add a group': a name, a 'Must pick' tick, a 'Max picks' number, and a row per choice with its extra charge. Nothing about your existing items changed — they were always stored as proper records, the text box was only how you typed them. The one-line format is still used by the Excel import, where a single cell has to carry a whole structure.