My MacBook Air M1 frozen when using full screen

Hello, I've had my MacBook for a month and everything is fine but when I use youtube with the full screen mode and click something from the menu bar (or if the safari window is in half and then I put the full screen mode) then the MacBook screen freezes, and I can't even control the screen brightness but for example if I click the video with the mouse it stops it, so it's like the computer is working but the screen is frozen. The only way I can "fix" this is by turning off the computer. Could you help me with that?

Pd: I forgot to mention that this only happens when I am using an external monitor, I've trying to replicate that without the monitor and it doesn't freezes.