Blender only illuminates the background?

There are various possibilities for this. Basically, you can either completely separate the two levels (left), or only influence how the light works (right) || All objects are white; the coloring comes through the light:

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Controlling influence from light1:

For each object that emits light, you can define which other objects are to be influenced by it.

I have created new collections for the filling light and pulled the corresponding objects from the outliner into them (drag & drop). Enable / disable the influence. Here it is only set for the background that light is received; only the podium, but not Suzanne, casts a shadow:

https://docs.blender.org/manual/de/4.3/render/lights/light_linking.html

[1] This feature has existed since the version 4.0 in Cycles and since 4.3 in EEVEE.

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Separate:

To do this, you can create multiple “view layers”. These control in the composite which objects are rendered in which output.

I created “scene” and “background” at the top right. Then in the Outliner (here under the View Layers) excl. activate the appropriate collection (which you have to create beforehand). The same for the second view layer (change to the top right in the menu).

Due to the fact that the lights for the background/model are in the corresponding collections, they only influence other objects in the same.

In the Compositor (left in the picture), you can then switch between the two layers and these e.g. as here:

https://docs.blender.org/manual/de/4.3/render/layers/introduction.html