If I create a 3D game object, I can't see the inside view of it

For example, if I create a cube, it should look like a room when I zoom in, but it doesn’t

This is because most shaders in Unity (all other game engines as well), by default, use Graphics optimization technique called Back-face culling

You can use Two-sided shader but expect it’s normal vector to be wrong (broken surface lighting on these back faces).