After generating MIDI data on an instrument track using Project/Chord Track/Chords to MIDI in Cubase Pro 14.0.10 (on Windows 10), attempting to edit the MIDI data in the Key Editor (both lower zone and full screen) did not work.
For example, I selected all the notes generated, then tried Shift-UpArrow (I needed to transpose the notes up 2 octaves to fit the range with a virtual guitar plugin that interprets chords from notes in a specific range), and nothing happened. I then tried manually dragging, and it looked like it would move the notes, but after releasing at the right point, nothing happened again. I even tried just moving a single note at one point, again with the same result – no change.
I finally ended up working around the issue by moving the generated MIDI to a new MIDI track, transposing it there, then moving the MIDI back to the instrument track (which was now empty since I moved the data rather than copying it). After that, I could edit the data.
Thus, short of some fluke with my specific project, or the specific Cubase session, it looks like there is something funky about the MIDI generated by the Chords to MIDI function. (I was looking for any sort of unusual visual indication, such as a lock icon on the clip, that might give a hint, but I didn’t find anything unusual.)