Steps to reproduce the issue

Run the following code:

$mailer = Factory::getContainer()->get(MailerFactoryInterface::class)->createMailer();
$mailer->setSender('test@example.com');
$mailer->addRecipient('me@example.com');
$mailer->setSubject('Test');
$mailer->setBody('Test body');
$mailer->send();

Expected result

The From header in the mail is test@example.com.

Actual result

The From header in the mail is the global from option from the global configuration.

System information (as much as possible)

Bug is since #46431 got merged and shipped with 5.4.2.

Additional comments

If other extension developers come across this issue, the fix is:

if ($mailer instanceof Mail) {
	$mailer->Sender = $mailer->From;
}