Changes the size of the Scratch stage from 480x360 (4:3) to something else.
Most projects will not work properly with custom stage size.
640x360 will make a widescreen 16:9 stage. Using higher resolutions such as 1280x720, 1920x1080, or larger is technically possible, but we recommend using a lower resolution with the same aspect ratio and allowing fullscreen mode to upscale it to the user's display (remember that some displays might not even fit such large stages!).
Projects can detect the stage size using methods such as https://scratch.mit.edu/projects/588493413/