Not just transport but all processes in the supply chain after the food leaves the farm — processing, transport, retail, and packaging — mostly account for a small share of emissions.

This data shows this is the case when we look at individual food products. However, studies also show that this holds true for actual diets; for example, researchers Vilma Sandström and colleagues studied the footprint of diets across the EU. Food transport accounted for only 6% of emissions, whilst dairy, meat, and eggs accounted for 83%.

https://ourworldindata.org/food-choice-vs-eating-local