New monitor doesn't work with games, why?

I bought a second screen for my laptop on Amazone (AOC, 24 "). I connected the screen to the laptop with an HDMI cable. It actually works really well but as soon as I open a game (LOL, Destiny 2, …) it starts the screen is spinning… I see flickering, then it briefly turns black and then it goes again and then not again, what could be the problem and how can I fix it?

Sry for misspellings.

And thank you in advance for your answers.

Try switching off the laptop screen so that the game only runs on the external monitor. Maybe your graphics card is overwhelmed when gaming when the LCD screen on the laptop is still on.