Setting the default Container width

By default, the Container block width is set to 1100px. If you’re using GeneratePress, it will default to the Container width option you’ve set in the Customizer.

If you’re not using GeneratePress and want to set a different default width, you can do this:

add_filter( 'generateblocks_defaults', function( $defaults ) {
    $defaults['container']['containerWidth'] = 1200;

    return $defaults;
} );