Collapse and expand layers
You may want to quickly collapse a layer to hide its events in order to focus on other layers.
You can do that by clicking the up/down arrow beside the layer's name on the timeline:
Collapsed layers continue to be displayed when you export your timeline as an image or PDF or share it with others. Think of it as a way to view fewer layers while you're working on your timeline, but not as something that impacts how it is seen by others.
To hide a layer from others, use the Hide Layer feature.