MacBook Pro + second monitor: picture freezes, sound continues (video lags)

Hello!

I got a question ... 🫣

When I use my MacBook together with a second monitor and set the external display as the main screen, while the MacBook display is used as an extended display, picture lags occur repeatedly when playing videos (e.g. on YouTube or Netflix). The picture freezes for approx. 2-10 seconds while the sound continues to play normally.

What can I do about this?