Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

https://www.php.net/manual/en/migration80.incompatible.php
> PHP Data Objects 
>
> * The default error handling mode has been changed from "silent" to
> "exceptions". See Errors and error handling for details.

https://www.php.net/manual/en/pdo.error-handling.php

I try set PDO::ATTR_ERRMODE = PDO::ERRMODE_SILENT and on php 8.0.1 it generates warning. But on php 7.4 warning does not appear.
https://monosnap.com/file/1xVCHwlg4APTzIhDZdfRcF889HTTLu

Code Example:

<?php
$dsn = 'odbc:WEB-TRUNK';
$user = '';
$password = '';

print '<pre>';
var_dump('error_reporting: ' . ini_get('error_reporting'));
var_dump('display_startup_errors: ' . ini_get('display_startup_errors'));
var_dump('PDO::ATTR_ERRMODE: PDO::ERRMODE_SILENT');
print '</pre>';

try {
    $dbh = new PDO($dsn, $user, $password);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_SILENT);
    echo $dbh->quote("test");
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

phpinfo();

> I try set PDO::ATTR_ERRMODE = PDO::ERRMODE_SILENT and on php
> 8.0.1 it generates warning. But on php 7.4 warning does not
> appear.

PDO_ODBC never supported quoting[1], so calling ::quote() is
useless.  Prior to PHP 8.0.0, there was a quoter function which
always failed; as of PHP 8.0.0, this quoter function has been
removed[2].  This is why you are seeing the warning now, but not
before.

[1] <https://www.php.net/manual/en/pdo.quote.php>
[2] <https://github.com/php/php-src/commit/24e2ba26b457da2c93aae75c7193c519b5a0aed9>

The PHP documentation still describes that PDO::quote() will return false if the function is not supported by the PDO driver. It also does not state a warning or exception could be thrown. (https://www.php.net/manual/en/pdo.quote.php)

Is the current behavior then considered correct? If so, should the documentation be updated?

The warning is due to bug #71941.