When did fungi likely appear, and what is the prevailing theory about their origin?

Origin of Fungi:

Based on paleontological data, scientists hypothesize that fungi emerged approximately a billion years ago. Currently, the majority of specialists believe that fungi evolved from various primitive single-celled organisms. These ancestral organisms lived in the primordial water bodies of our planet, and at that stage, it was difficult to classify them as strictly plant or animal.

The Colonization of Land:

The first fungi were unicellular, and later multicellular fungi appeared. Some theories suggest that the "age of fungi" began when living organisms started colonizing land. Before this period, only aquatic fungi existed, and some still do today. It is highly probable that fungi were the first to master terrestrial life, settling in coastal areas long before the plant kingdom did.