The Rendertarget image captured by SceneCapture2D is very dark!

The Rendertarget image captured by SceneCapture2D is very dark, almost entirely black!
I have looked through a lot of information and methods, and the only effective one is to change the Capture Source to Final Color (LDR) in RGB, but it cannot use Alpha. Therefore, I want to use SceneColor (HDR) in the RGB series, but it seems to have no effect; the image is always very dark! Is there any way to solve this problem? It is very important to me!
I also tried the PostProcess Volume and PostProcess settings in Scene Capture, but nothing worked. I have also changed the value of Target Gamma in the RenderTarget, but it seems to be of no help!