The proposed solution is correct ... but it is not the good way to deal the problem.
In fact, Symfony should not try to delete sessions, it is generally a system's responsibility.
The mistake was that Symfony (before 7.2) overrides php.ini 's configuration.
Please check : https://symfony.com/doc/current/reference/configuration/framework.html#gc-probability
The solution is to set it to 0 for desactivating Symfony's cleaning.