This just happened to me... I can't figure out how to get it back. All i did was press command+T and it disappeared. Can you explain what "issuing a defaults delete com.apple.dt.Xcode" command is?

This fixed it for me. When apple logo appears, press volume up, then volume down, then press and hold the side button. When I did this it made me plug in my phone to my computer and update the phone. This puts the phone into recovery mode. These videos were helpful for me: Random youtuber - youtube.com/watch?v=C5VWYbIH49s OR Apple Support - youtube.com/watch?v=2CRilTPouRU