Unity provides multiple Skybox Shaders for you to use. Each Shader uses a different set of properties and generation techniques. Each Shader falls into one of the following two categories:
Textured: Generates a skybox from one or multiple textures. The source textures represent the view of the background from all directions. The Skybox Shaders in this category are:
Procedural: Does not use textures and instead uses properties on the Material to generate a skybox. The Skybox Shader in this category is:
The Built-in Render Pipeline, and the Universal Render Pipeline (URP) both exclusively use skyboxes to render a sky. They both support all of the above Shaders.
The High Definition Render Pipeline (HDRP) does not support any of the above Shaders and instead includes multiple sky generation solutions.