You have to select the objects in the Timeline — not the object manager or editor. Make sure the Timeline is in automatic mode and that “show all animated” is active (both under the Timeline>View menu).
The f-curve manager is just another mode of the timeline, you can switch by clicking on the key icon at the top of the timeline, which will then switch to a sin wave icon, indicating you’re in f-curve mode (or uncheck View>Key Mode).