I am entirely new to SL. I am running SL 13 Pro and I am experimenting around with its features and tools. I trying to pitch shift a selection. I make a time-based selection and select Transform Selection. I then change the pitch, lowering it by 4200Hz. When I play back the selection, nothing has changed? What secret handshake am I missing here?
Mind that you are using the Transform Selection tool in your screenshot (hollow/black cursor icon), which is solely meant to change the selection area itself, but not the actual audio data the selection covers.
To change the audio data, you have to use the Transform tool (solid/white cursor icon) or use Edit → Transform.
When using the Transform tool, you can either drag or resize the selection directly within the spectrogram and you should get a preview immediately, or you enter a value in the top bar and confirm with the [Return] key on your keyboard.
The Transform tool will automatically transform the currently selected area, or the whole layer if there is no selection.