NT-incremented-ID.php

add_filter('ninja_tables_item_attributes', function ($attributes) {
    $latest = ninja_tables_DbTable()->where('table_id', $attributes['table_id'])->orderBy('id', 'DESC')->limit(1)->first();
    $value = json_decode($attributes['value'], true);

    if ($latest) {
        $latest = json_decode($latest->value, true);

        if (isset($latest['id']) && isset($value['id'])) {
            $value['id'] = $latest['id'] + 1;
        }
    } else {
        $value['id'] = 1;
    }

    $attributes['value'] = json_encode($value);

    return $attributes;
});