Maybe what is happening is before 2020 the people who carried the food from the kitchen to the customer were employees and after the people who carried the food from the kitchen to the customer are gig workers not employees which would explain "Figure 1. Annualized Real Sales per Employee (1992=100), Food Services and Drinking Places, Seasonally Adjusted" [0]. Restaurants now use gig workers and not employees to deliver the food. Of course, there are more sales per "employee."

[0] https://imgur.com/a/3n1ZJku