If there is a planet as big as the sun to live in, it can't exist, because the earth-like planet has a mass limit, at most, the super earth has reached it, and its mass is several times that of the earth. Rock celestial bodies can't be bigger than stars. There are many reasons why the earth is suitable for human survival, not to mention that the earth-like planets can't reach the size of the sun in terms of mass or volume. From the perspective of pure imagination, the most important thing I can think of is the acceleration of gravity. The average gravity acceleration g of the earth is 9.8m/s 2, which varies with latitude and altitude (essentially determined by the distance from the center of the earth and the axis of rotation of the earth).

If we ignore the factor of rotation, according to the law of universal gravitation, the acceleration of gravity is directly proportional to the mass of the planet and inversely proportional to the square of the radius of the planet. Therefore, the acceleration of gravity is essentially a binary function about the mass and radius of the planet. Whether there is a suitable gravitational acceleration on the planet surface depends on the ratio of its mass to the square of its radius. As long as the proportion is appropriate, the mass and volume are slightly larger and smaller, which will not have much influence on the acceleration of gravity. This is another constraint, but only if the mass does not exceed the gas planet.

At present, the earth-like planets discovered are super-earths, which are several times more massive than the earth, and then will be ice giants and gas planets. None of these planets has a solid surface, so there is no human habitation. But there is one exception, and that is Dyson sphere. If there is a planet as big as the sun that can live in, it must live in Dyson circle. Such a civilization also exists in theory. Then human beings live on the surface of Dyson sphere, and the inside is a device for collecting energy, so there is no sun in the sky.