Merging meshes in the hierarchy In the hierarchy, I have two meshes called "Cube" that I'd like to merge together:



Most answers that I've found online say to Shift select both and press Ctrl+J to merge them. However, weirdly that doesn't work in my case. If I select both the green triangles with dots and press Ctrl+J, nothing happens. If I select both of the yellow triangles and press Ctrl+J, nothing happens. If I select all four of these and press Ctrl+J, nothing happens. In all of these situations it's as if I wasn't pressing J at all, nothing changes on screen.

Is there something weird about my situation that would cause Ctrl+J to not work?

It's especially frustrating that Blender 2.8 doesn't give any errors or any reason why it's not joining the meshes as I wish it to.
As per @Edgel3D's advice and my own experimentation, it seems that it's impossible to merge meshes in the hierarchy. All merging must be done in Object Mode in the 3D view, or else nothing will happen.

Hopefully this helps someone else who had the same problem and is wondering why Ctrl+J isn't working.