A Full-Width image means the image spans from right to left and takes the full 100% of the screen's width. There are numerous ways to create an elementor full-width image.
To begin with, set the image as the section background
To create an elementor full width image, you need to set the image as the background of the section you want the full width image to be then you set the position to center center, and repeat to no repeat
Then, if you want a full screen hero section, set height to 100vh
To create a full page background image in Elementor, it is the same process with creating a full-width background image, you just need to need to click on height and change the minimum height to 100VH.
Finally, if it doesn't cover the entire screen, check your template settings
Some template settings, mostly from themes other than 'Hello', like Astra, need to be set to 'full width' to display properly.