skybox do not change ambient light

if I change skybox before game start by assigning reference,
when game start, ambient color is changed.
But if I change skybox by script, the ambient color is the same as before even if the skybox has been changed.
How could I Change ambient through skybox?
Do I have to do some settings by script?
Thanks for reading my poor english.

@Tsinning I read the documentation and maybe this can help:

You can also specify when Unity updates the ambient lighting. To do this, change the Ambient Mode. The two values are:

Realtime: Unity constantly regenerates ambient lighting for your Scene. This is useful if you alter the skybox at run-time
Baked: Unity only generates ambient lighting for your Scene when you click the Generate Lighting button at the bottom of the Lighting window. This is useful if your skybox does not change during run-time because it saves computational resources.

I have the same problem. The option for realtime ambient light doesn’t show up in the Rendering/Lighting menu. Is this setting maybe not available in URP?