UPGRADE

v3.x > v4.x

Changed compatibility to PHP 8

Changed localizeddate to format_datetime

When upgrading from v1.x to v2.x you should(must) do the following if they apply to your case:

The parameters entered in config.yml are not used anymore as they are managed by c975L/ConfigBundle, so you can delete them.
As the parameters are not in config.yml, we can't access them via $this[->container]->getParameter(), so you have to replace $this->getParameter('c975_l_exception_checker.XXX') by $configService->getParameter('c975LExceptionChecker.XXX'), where $configService is the injection of c975L\ConfigBundle\Service\ConfigServiceInterface.
The exceptionCheckerSecret is now managed by c975L/ConfigBundle, so you can delete it from parameters.yml and parameters.yml.dist, but before that, copy/paste it in the config.
Before the first use of parameters, you MUST use the console command php bin/console config:create to create the config files with default data.