Why Won't this Object UV Unwrap? I'm using Blender 2.83.1, and one of the objects in my scene won't UV unwrap. Every other object in the scene is ok, except the one. I've:

Applied Rotation, Scale, Position
Cleaned up the mesh
Removed Doubles (merge by distance)
Set the Origin to Geometry

Every other object in the scene and new objects all unwrap with no issues, so I don't think it's my UV settings. I've removed all modifiers and textures and shaders, but I still can't unwrap it. I know the object in question is one that I could easily recreate, but I'd like to know what happened before it happens to a much more complex object not so easily remade. I'd be grateful for any advice on this!
Here's a link to the file (thanks Batfinger, for telling me about this!):

UPDATE:
Thanks for testing the file, everyone! It helped me narrow down the problem (my nooooobishness) once I knew the file or Blender wasn't corrupt. For all of the other objects in my file, I could mark a seam in edit mode, click &quot;A&quot; to select all, and click &quot;U&quot; to unwrap the object in the UV editor. For this object, I had to click &quot;UV&quot;&gt;Unwrap to unwrap this object. I'm not sure why this object was different than the rest, but that's 'cause I a noob. I'm sure I'll learn what I did in time! Anyway, thanks again, everyone! –
Unwrap shortcut U in UV Editor works only if any UV Map already exists.
If in Properties Editor &gt; Data &gt; UV Maps is not listed any, it does nothing.

By default new objects are unwrapped, so if you modeled them and then just updated UV Map it works from UV Editor as well.