When you connect a TV or projector to your Mac to present you will want to extend your desktop as opposed to mirror your desktop. Extending your desktop allows you to place a separate presentation window on the second screen while keeping the TrialPad interface on your primary screen.
Details on connecting multiple displays can be found here:
https://support.apple.com/guide/mac-help/connect-an-external-display-mchl7c7ebe08/mac
Details on the settings to select can be found here:
Then in TrialPad, when you click the Output switch to On an empty presentation window will appear ready to display your evidence. You can move this presentation window to a TV or projector screen by dragging the window by the top bar (just to the right of the red/yellow/green “traffic light” window buttons), and then have the presentation window fill the screen of the secondary monitor by clicking on the green traffic light button. Once the presentation window fills the screen the traffic light buttons will disappear but you can view these buttons again, and bring the window back to the original size, by moving your mouse to the top area of the window to reveal the traffic light buttons again and clicking on the green window button.