Hi Mamun
you can remove the sidebar from the 404 with this snippet:
add_filter( 'generate_sidebar_layout','tu_custom_search_sidebar_layout' );
function tu_custom_search_sidebar_layout( $layout )
{
// If we are viewing 404 message, set the sidebar
if ( is_404() )
return 'no-sidebar';
// Or else, set the regular layout
return $layout;
}
https://docs.generatepress.com/article/adding-php/
Or you can use this CSS:
.error404 .sidebar {
display: none;
}