eager to learn wrote:I was reading you can’t Undo your last task by just pressing Ctrl + Z (like you can in many Windows-based programs).
You can, but "Undo" works on changes or edits made to your project, and what the OP is asking about is a change made to a
view of the project. If you change something in how you view the project (open or close the Inspector panel, for example) that is not something that gets undone by Ctrl + Z.
To the OP: if you have multiple timelines visible it means you have the "stacked timelines" view turned on. This is controlled by the view opens icon in the upper left corner of the timeline. In "stacked timelines" view you get an extra bar across the top of the timeline panel that has "tabs" for easy switching between different timelines. At the far right end of that bar there's an icon (windows with a little "+") to add another entire timeline inside the panel. If you click it, you get to view two timelines at once. When you've got multiple timelines visible, there's an additional icon at the right end of the tab bar (windows with a little "-") to remove a timeline from the panel - that's the one you want to click.