Error Reporting Itself

ini_set('display_errors', 1); or display_errors

Simply allows PHP to output errors - useful for debugging, highly recommended to disable for production environments. It often contains information you'd never want users to see.

error_reporting(E_ALL); or error_reporting

Simply sets exactly which errors are shown.

Setting one or the other will not guarantee that errors will be displayed. You must set both to actually see errors on your screen.

As for setting this up permanently inside your PHP config, the default for error_reporting is E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED. That said, this variable should not need changed. See here:

http://php.net/manual/en/errorfunc.configuration.php#ini.error-reporting

As for displaying errors, see here:

http://php.net/manual/en/errorfunc.configuration.php#ini.display-errors

Set the config value of "display_errors" to either stderr or stdout, depending on your need.

Just change these variables inside of your php.ini file and you'll be golden. Make absolutely sure both display_errors and error_reporting is set to a satisfactory value. Just setting error_reporting will not guarantee that you see the errors you're looking for!

Error Reporting Works Everywhere Except When Connecting To My DB!

If you see errors everywhere you need to except in the Database Connection, you just need to do some error catching. If it's PDO, do something like this:

try {
    $this->DBH->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );
    $this->DBH->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
    $STH = $this->DBH->prepare("INSERT INTO `" . $this->table . "` ($fs) value ($ins) $up");
            
    $STH->execute($data);
            
    $id = $this->DBH->lastInsertId();
            
    $this->closeDb();
            
    return $id;
} catch(PDOException $e) {
    echo $e->getMessage();
}

Just a snippet from my framework. Of course you'll have to change it to your liking, but you should be able to get the general idea there. They key is this part here:

try {
    //DB Stuff
} catch(PDOException $e) {
    echo $e->getMessage();
}

I Still Don't See The Error

If you've done both of what I've listed here and still have trouble, your problem has nothing to do with enabling error reporting. The code provided will show you the error with a Database Connection itself, and inside of PHP code. You must have a completely different issue if this has not shown you an error you're chasing.

You'll likely need to be a bit more descriptive on exactly what you're chasing, and what you're expecting to see.

Try:

ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

perhaps, it will help you. change values of parameteres in the file /etc/php/7.0/fpm/pool.d/www.conf (for example value display_errors by default is disabled)

I could find the errors in /var/log/php7.4-fpm.log