What is the best way to lighten up a scene via ambient lighting?

Per default, RealityKit scenes are way too dark. The only solution I could find for this problem so far was to add an image based light to it. But it looks pretty weird, if I use a central IBL. The shadows are way too strong, and if I increase the intensity, the highlights get way too light. If I attach a light to each object, it kinda works, but feels strange to do so. I could not find any option to just setup an ambient light. Isn't there a way to do this, or am I just too dumb?