AT:

• it exists a configuration option to enable/disable the "Java Serialization Data Format"
• by default the "Java Serialization Data Format" is disabled
• the new configuration parameter has affect only in case when vairables are set by their serialized representation
• the change is described in the upgrade guide [1] and [2]

Hint:

• the default serialization data format stays to JAVA - it is used when serializing object variables to store them in the database
• in case of the patches the "Java Serialization Data Format" should be enabled and the default serialization data format remains as it is

[1]: https://docs.camunda.org/manual/7.8/update/patch-level/#special-considerations
[2]: https://docs.camunda.org/manual/7.8/update/minor/