Help, my iphone keeps taking selfies when i open the messenger app

As title says, whenever I open the messenger app on my iPhone 15 pro max, it pauses, screen goes darker and a banner comes across the top of the screen saying

“when “messenger” is opened” is taking photo…

it then proceeds to take a screen shot a second u til I can manage to swipe the messenger app off which takes a while as each time I try to do this it pauses, goes dark and banner comes across and repeats

any ideas please