Behavior Transactions PDO::beginTransaction() and "BEGIN"

Question

I have a strange behavior in a php script (PHP 8.1) using MariaDB 10.7.5 database.

This one with native SQL works:

$pdo->query("BEGIN");
[ ... some database stuff ... ]
$pdo->query("COMMIT");

But using PDO's own function does not work, it results to "PHP Fatal error: Uncaught PDOException: There is no active transaction in xxxx":

$pdo->beginTransaction();
[ ... some database stuff ... ]
$pdo->commit();

Can someone explain me why?