I am using 2020.1
Unity will not use switch from solid color to a procedural Skybox while using URP.
I tried on an older version without URP and it works just fine.
not sure what the issue is.
Take a look at Window->Rendering->Lighting->Environment, Skybox Material, that might not be set to the material you want (or the material might not be using the shader you want).
Is the shader you want (I’m guessing “Skybox/Procedural”) selected for SkyBox? If you’ve had the same material while changing render pipelines / versions around the material might have somehow lost the original reference and changed to a built-in fallback.
Yes it is selected. Also I have noticed that if I go into project settings > graphics > and turn off URP. the skybox comes back.