Unity version - Unity 2021.1.12f1
Lightmap Lighting Mode - Bake indirect
Render Path - URP
All Objects in Scene are marked as static.
That's the indirect lighting you baked.
Because of the presence of the boxes, some of the surrounding bluish sky light is blocked from falling in those areas, making the surfaces there appear darker and less blue (more orange).
But also, some light bounces off of the orange boxes, taking on an orange colour, and lands in nearby areas, giving them an additional orange tint.
The parts underneath the objects should not be visible in gameplay, because the objects are "static" - you've made a promise to the engine that they are never going to move from their baked positions during gameplay. If these are objects that you need to move, then they should not be marked static.
These combined effects - simulating the blocking of light and the transport of coloured reflected light to nearby surfaces - is what indirect lighting and global illumination are designed to do. If you don't want these effects, then you might want to turn off any global illumination and stick to simple direct lighting.