What lies behind this picture of a dolphin is a mesh set to be a shadow catcher, so it can effectively product an image floating in space. I understand that in Blender 3 the shadow catcher function seems a little different than earlier versions. Is it rendering in a separate layer? Because I only see one.
Under "combined", it has a "ShadowCatcher" layer.
I notice that when I turn off the Denoise option, the shadow appears in the render.
When you see the Shadow Catcher pass in the render window's dropdown menu under Combined this means you have the Shadow Catcher pass enabled, which you find at View Layer Properties > Passes > Light > Other.
In this case, the Shadow Catcher will not be showing directly in the render but is a separate pass which you can use in the Compositor. For example to make it brighter or darker or color it somehow, or use it as some kind of mask etc.
If you do not want this and simply use the shadow catcher as before, disable the pass in the View Layer Properties and then the shadow will be fixed in the rendered image. In this case if you want to composite the shadow with a different brightness or color etc. you have to mask it out manually.
