I am relatively new to Blender animation. I find myself unable to move or delete keyframes in the Dopesheet Editor. I also see that they have a ghosted appearance. How do I change these keyframes (back?) to an editable state once more?
I figured it out. I had Appended the character Armature from a different .blend scene file. Whether by accident or design, this Action (highlighted in the sample image) came in as "linked". This means it is "linked" to the data in that other file and would only change if the action were changed in the source file and then re-evaluated here, locally. The benefit of this is that the animation could be stored in an Action, re-used in multiple other scenes and then updated in one place, with the change then propagating out to the Linked scenes. In my case, looking at the list of Actions revealed one that had a small icon next to it of a small chain (see image). In the second image, I have selected that Action and hovering on the chain icon revealed that I could "click to make local". I did so and can now edit the keyframes as-expected.
Less than one year into my transition to Blender, I see that I have a lot to learn.