how do i support 90fps on my device. why 60 fps. I want 90 fps
Are you talking about the display refresh rate? You can change it in the quick settings menu. (60/90/120/144 Hz modes are available on the ROG Phone 3.)
Edit: The option is not added to the menu by default, you will have to add it yourself. You can also go to Settings -> Display and change it from there.