Symfony 6.1.1, the latest version got released on June 09, 2022 and is reported to be stable.
What is Symfony?
A PHP web application framework, Symfony has a library of reusable PHP components. Licensed under MIT, it was published as a free software first in October of 2005.
Fabien Potencier created Symfony as an open-source framework to create web applications.
What does this mean to Drupal?
Drupal 10 is scheduled to be released on December 14, 2022. The December release also means Drupal 10 will be released with Symfony 6.2, which will have improvements and bug fixes over the current 6.0 version, and also will reduce the workload for Drupal Security Team.