allowMajorVersionUpgrade

A value that indicates whether major version upgrades are allowed.

Constraints: You must allow major version upgrades if you specify a value for the EngineVersion parameter that is a different major version than the DB cluster's current version.

If you upgrade the major version of a global database, the cluster and DB instance parameter groups are set to the default parameter groups for the new version, so you will need to apply any custom parameter groups after completing the upgrade.