I can't get SKU name for the title tag because of the not index product attribute?
The PHP error is because of the deprecated functionality
implode as on
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
Plugins or through
$sql = implode($parts, $this->type);
$sql = implode($this->type, $parts);
As you can see the arguments for
implode have been interchanged (swapped), which is the expected order of arguments as of
To properly override the respective Magento Framwework file, check the one below
How to override Magento 2 framework file?