Ever since my first flight, the option to control my gimbal has disappeared and I can no longer adjust the camera angle. Am I missing something? Is there an option I hit to hide it?

All I can think of (other than a hardware malfunction) is to ensure that the camera is set to follow and not FPV in the gimbal setting options.

It is the scroll bar on the right.  Next to the shutter button.  Additionally, you can hold the screen or press sensitive the screen harder, to select the gimbal moving with phone tilt.  Lastly you can scroll the wheel on the back of the remote to tilt.

Sir, please tell me the model of your mobile device and the version of your app. I would recommend you save all the files and reinstall the app. Please follow the advice above and check if the camera can tilt up and down by long pressing the image screen. Thanks for your support.