Is a mushroom an autotroph?

Mushrooms are heterotrophs. They are not plants or autotrophs.

Every living thing that exists need energy in order to live. This energy ultimately comes from the sun, and only plants, or autotrophs, can directly use this energy to make food. Those organisms that cannot harness the sun's energy are known as heterotrophs.

Mushrooms belong to kingdom Fungi and are heterotrophs because they decompose and consume nutrients from the soil. They are not green so they cannot photosynthesize

For this reason, mushrooms and all other fungi are heterotrophs.