Welcome to the community Fernando!
By far the biggest issue with the outliner right now in my opinion. Closely followed by the absence of manual sorting.
It was proposed many times on right click select as well as here. As far as I know there was some discussion about there being too many highlighting types as is, and this was abandoned/put on hold.
A pity really. I work with heaps of people in production and every single one of them is confused/discouraged when bumping into this.