I was initially baffled into starting to write this post, when I saw that these three specific choices were grayed-out on the “Add” popup: “Add Camera,” “Add Speaker,” and “Add Text.”
Then, while writing this, I “figured it out.” I was in Pose Mode.
However, this leads to a follow-on question (2.7): “in Pose Mode, why can I add anything?” If all the choices had been grayed-out, I would have quickly guessed “a mode.” But, instead, these only.
I’m scratchin’ my head here to figure out in what “real” situation such an odd selection of choices would make sense.
Note that I did not actually attempt to add anything at this point.