[@robin-w Moderator 5 years, 11 months ago]

your theme or elementor is doing this

it has a css entry

.has-sidebar:not(.error404) #primary {
	float: left;
	width: 58%;
}

you could change this to 100% in your custom css ie put this in your custom css

.has-sidebar:not(.error404) #primary {
	width: 100% !important;
}

but it might affect other parts of your site, so try it and see