Step 1: Apomixis is reproduction that produces seeds without the fusion of gametes. Three well known routes to this are diplospory, apospory, and adventitious embryony, each skipping true fertilization in a different way.
Syngamy, by definition, is the union of male and female gametes to form a zygote. That is exactly the sexual process apomixis is designed to bypass.
Therefore syngamy cannot be classed as a form of apomixis; it belongs to normal sexual reproduction.
Answer: Syngamy.