On this site.
The banner is an image in the HTML image tag.
But in our theme, your banner is a background image in a div.
An image in HTML tag and a background image in a div behaves differently.
Yes, if you have an image in HTML tag and not as a background div, it will be much easier to handle.
But this will require modifications to the theme code.
Our support does not include providing assistance in modifying theme codes.
You can contact us for customization service via https://theme4press.com/theme-customization-service/
Or you can use multiple sets of media query css to fix it in different browser widths, which is why I asked for viewport sizes.