scalar localtime((stat($filename))[9]) is not a variable (although its result varies, of course), so I guess variable interpolation doesn't help here.

Here, I'd use the string concatenation operator, like this:

    text =>$config_data[$i][0] . " Information Last Updated at: " . lo
+caltime((stat($filename))[9])
    );
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My perl is a bit rusty (peak use was at the turn of the century), but AFAIR the scalar can be omitted here