Weird! Have you tried clicking the “Preview” button top left? It looks like it is not in preview mode either. (I don’t do sound - do you need a camera with an Audio Listener for sound to work normally?)
welp, i booted it back up to take a look and it was on the empty timeline tab. i read the mumbo jumbo it said about adding a director and timeline asset. never heard of that. but ok, thanks to you i clicked the camera and then the “create” button it had for me there in the middle of the empty timeline, and what do u know, it has a playhead now. no idea what any of this means, but cool. and thanks to you too buddy.
didnt know why i needed a “playable director” on my camera for a timeline to work, or why nothing mentioned this before anywhere else. i never read those stupid little messages. i assumed it said “select a timeline for it to show up”, like no friggin kidding right? but can you believe it actually had something useful in it to read? pretty amazing. i hope this means its working now. what a stupid overlooked design choice on Unity’s part. they always have these weird combinations of things you have to setup for anything to work properly.
Well, you see… umm. Okay, I don’t understand that either! 
My cameras do not have a playable director. Instead, I have an empty game object in the hierarchy that I put the Playable Director on that is a handle to the “Timeline” in the scene hierarchy. The Playable Director component has a reference to the “Playable” (Timeline Asset) and also is where the bindings for tracks are stored. Timeline assets can be bound to different game objects. I don’t really understand why someone wants to reuse a Timeline for different objects, but I think of it like you can choose your own avatar when you play a game, so you need to be able to drop different characters into the Timeline based on what the user wanted. The bindings bind games objects in your scene to the Timeline Asset (which is a file on disk, not a part of the scene).
The audio side I have never used (!). I create silent cartoons with speech bubbles. I just find when I create a camera it has an Audio Listener component on it. Doing a Google Search it says “The Audio Listener acts as a microphone-like device. It receives input from any given Audio Source in the scene and plays sounds through the computer speakers…” So it sounds potentially important to make sound work.
But I have another theory with Unity. If its working, don’t touch it!
Unity’s “documentation” on the subject is a joke. another monkey-run company.
p.s. i found some documentation from 2017. something like a simple timeline should not be this complicated to setup. JEEZ
10 things plug into another 10 things into another 10 things. this is ridiculous. id be better off programming my own timeline from scratch.