Source

File: wp-includes/blocks.php

function _excerpt_render_inner_columns_blocks( $columns, $allowed_blocks ) {
	$output = '';

	foreach ( $columns['innerBlocks'] as $column ) {
		foreach ( $column['innerBlocks'] as $inner_block ) {
			if ( in_array( $inner_block['blockName'], $allowed_blocks, true ) && empty( $inner_block['innerBlocks'] ) ) {
				$output .= render_block( $inner_block );
			}
		}
	}

	return $output;
}