Question Issue with screen tearing/stutter on external monitor, but only when laptop display is off ?

Hello, I usually don't have to post questions like this because I mostly am able to figure this stuff out. This is a weird one for sure and hopefully someone has an idea of how to fix it, I will give a break down of what I have tried and what the issue is to the best of my ability's.

System: Dell G7 7700 17" 2070 Max P 125 Watt.

I have tried 3 different 144 hz to 165 hz monitors G-sync enabled and disabled. I have tried all of this on HDMI, USB C and DisplayPort.

When I am using the laptop by itself there's no tearing/stuttering, works great.

When I am using external monitor with the laptop screen also on, there's no tearing/stuttering, works great.

But If I turn the laptop screen off ,games all tear/stutter horribly even with 100+ fps on the external monitor ?

I am running out of idea, There is no reason for the laptop screen to be on when I am using an external monitor.

Any ideas will be helpful, Maybe I am missing something simple.