www.magento2.com/Category1/Category2/gear/bags.html

www.magento2.com/bags.html

protected function isNeedToGenerateUrlPathForParent($category)
{
    return $category->isObjectNew() || $category->getLevel() >= self::MINIMAL_CATEGORY_LEVEL_FOR_PROCESSING;
}

const MINIMAL_CATEGORY_LEVEL_FOR_PROCESSING = 3;

class RemoveParentCategoryPathPlugin
{
    public function aroundGetUrlPath($subject, $proceed, $category)
    {
        if (in_array($category->getParentId(), [Category::ROOT_CATEGORY_ID, Category::TREE_ROOT_ID])) {
            return '';
        }
        $path = $category->getUrlPath();
        if ($path !== null && !$category->dataHasChangedFor('url_key') && !$category->dataHasChangedFor('parent_id')) {
            return $path;
        }
        $path = $category->getUrlKey();
        if ($path === false) {
            return $category->getUrlPath();
        }
        return $path;
    }
}

$allCategories = $categoryCollectionFactory->create()->load();
foreach ($allCategories as $category) {
    $category->setDataChanges(true);
    $category->save();
}

vendor/magento/module-catalog-url-rewrite/Model/CategoryUrlPathGenerator.php around line 75

/* if ($this->isNeedToGenerateUrlPathForParent($category)) {
            $parentPath = $this->getUrlPath(
                $this->categoryRepository->get($category->getParentId(), $category->getStoreId())
            );
            $path = $parentPath === '' ? $path : $parentPath . '/' . $path;
            $path = '';

        } */

/* if ($this->isNeedToGenerateUrlPathForParent($category)) {
            $parentPath = $this->getUrlPath(
                $this->categoryRepository->get($category->getParentId(), $category->getStoreId())
            );
            $path = $parentPath === '' ? $path : $parentPath . '/' . $path;
            $path = '';

        } */