When I select an object in 3D view, how can I see the object highlighted in the Outliner if I have placed the object in a Collection?
Your object is represented by that upside-down delta (triangle) shape. See how it's highlighted with a light grey box? That's it.
Everything inside a collapsed collection is represented by icons next to its name - meshes with this triangle; cameras, lights, etc. have their own symbols which are colour-coded too. If one of them is selected, you get the little grey box around its icon.