The Sun does not have a solid surface like a planet. Instead, it is composed of extremely hot and dense gases in a state known as plasma. The outer visible layer of the Sun is called the photosphere, which is where most of the light and heat we receive from the Sun originates. However, the Sun's plasma extends well beyond the photosphere, transitioning into the outer layers of the solar atmosphere known as the chromosphere and the corona.
As for whether the Sun can become a planet, the Sun itself cannot transform into a planet. Stars like the Sun are massive celestial bodies primarily composed of hydrogen and helium gases that undergo nuclear fusion in their cores, generating immense energy. Planets, on the other hand, are much smaller and predominantly made up of solid or rocky material. They form from the material left over after the formation of a star, known as a protoplanetary disk.
In the early stages of the solar system's formation, the Sun initially began as a collapsing cloud of gas and dust called a molecular cloud. Gravity caused this cloud to contract and heat up, eventually forming a protostar. Through the process of gravitational collapse and accretion, the remaining material in the protoplanetary disk coalesced to form planets, moons, asteroids, and other objects.
The Sun, being much more massive than any of the planets, gathered the majority of the material in the protoplanetary disk, leaving behind only smaller objects as planets. Thus, the Sun has always been a star throughout its history, and its formation was a separate event from the formation of planets.