I have main screen playing games like Euro Truck Simulator 2 and the other screen with discord but when playing the game it won't let me move from 1 screen to another I've searched your forum couldn't find the answer couldn't even find answer on Google

There are many posts to do with this and similar here is one of them:
https://www.displayfusion.com/Discussions/View/this-would-be-a-nice-feature-play-on-one-monitor-surf-on-another/?ID=08440b0a-51e2-43ee-8c50-3795a5fd1a7a

In short you would still have to press the assigned key but it will leave the game screen in full size.

OK thanks for the link