flattenblocks.php

<?php

function flatten_blocks( array $blocks ) {
    reset( $blocks );

    $out = [];
    
    while ( $block = array_shift( $blocks ) ) {
        $out[] = $block;

        if ( ! empty( $block['innerBlocks'] ) ) {
            array_unshift( $blocks, ...$block['innerBlocks'] );
        }
    }

    return $out;
}