A number of ways:

https://telepromptermirror.com/mirror-flip-screen/

Personally I gave up on the window flippers and use LunaDisplay w/ iPad.

Why? The window flippers flip the window — but not the mouse or button click targets! So you need the whole screen to flip, not just the window.

Tried out the WindowMirror utility and the click targets are indeed pretty confusing… but it might still come in handy when presenting. With the looks of it, I could use it to flip a windowed OBS projector view, and drag that to the external monitor that is my teleprompter. Wouldn’t need to click much in that scenario. Thanks!