A Solo is similar to a group, but only one of the elements inside the solo is rendered at a time. This is much faster than having to animate the opacity of each object individually.
There are two ways to create a solo. The first is to select multiple items on your artboard, right click them in the Hierarchy, and click “Wrap in Solo”.The second option is to select the Solo tool from the Hierarchy Tools dropdown (or click S on your keyboard) and click anywhere on your artboard. Now that you have a Solo in your Hierarchy, you can drag elements into it.
Sometimes when we animate an object or character, we need to create animations at different angles. Solos allow us to create multiple rigs and switch between them during our animation.