Magento2 - Product Attribute Not reindex error

Question

I can't get SKU name for the title tag because of the not index product attribute?

Answer 1

The PHP error is because of the deprecated functionality implode as on PHP 7.4.x

8.0.0 Passing the separator after the array is no longer supported.

7.4.0 Passing the separator after the array (i.e. using the legacy signature) has been deprecated.

You need to replace the line in the file Magento\Framework\DB\Sql\UnionExpression inside the method __toString() through Plugins or through preferences

$sql = implode($parts, $this->type);

with

$sql = implode($this->type, $parts); 

As you can see the arguments for implode have been interchanged (swapped), which is the expected order of arguments as of PHP 7.4.0.

To properly override the respective Magento Framwework file, check the one below

How to override Magento 2 framework file?

PHP implode