Add a containing DIV to core Gutenberg blocks

I’m sure there are other ways e.g. with CSS only or Add custom class to core blocks in Gutenberg, but regarding:

Add a containing DIV to core Gutenberg blocks

one way could be with the render_block filter:

add_filter( 'render_block', function( $block_content, $block ) {
    // Target core/* and core-embed/* blocks.
    if ( preg_match( '~^core/|core-embed/~', $block['blockName'] ) ) {
       $block_content = sprintf( '<div class="some__class">%s</div>', $block_content );
    }
    return $block_content;
}, PHP_INT_MAX - 1, 2 );

to div-wrap the core blocks on the frontend.

Changing the HTML layout might affect the current style of the site.