Checked the profile of a good friend of my, who runs his own business, but has no background image (bg img), so here is a humorous list why you have to have a bg img.
The recommended size for a LinkedIn background image is 1584 pixels (px) wide by 396 px high.
However, the image will be automatically resized and cropped to fit the space, so it's best to upload an image that is at least 1584 px wide to ensure it looks good on all devices.
The maximum resolution for a LinkedIn background image is not 20000 px × 20000 px.
The maximum resolution for a LinkedIn background image is 8MB.
Create with Canva, for free :)