On this page of the Baldurs Gate 3 guide you will learn how to highlight interactive objects.
As you explore the game world, you can come across a number of functional elements. These could be bodies to search, crates concealing valuables or books. The cursor informs about whether we can perform an action on a given object and what type of activity it is. When you point the cursor onto something interactive, it changes its appearance.
Often you will find several such points on the screen at the same time. Some of them are hard to miss, but the rest may be harder to spot. Therefore, the game has a special key that when pressed highlights the interactive objects currently on the screen. This is the "ALT" button by default, but you can change it in the game settings. In addition to highlighting the objects themselves, it also informs about their type.
However, you have to bear in mind that this method does not always highlight all the objects on the screen. There is no rule as to the type of object that is illuminated. So make sure you don't miss something.