To meet the specific requirements for record reassignment, you must use Configurable Cascading. Standard types like Parental (which cascades everything) or Referential (which cascades nothing) are too rigid.

• Cascade Active ensures that only "Active" (outstanding) tasks are reassigned to the new account owner.
• Completed tasks are considered "Inactive" in the system; therefore, under the Cascade Active setting, their ownership remains unchanged, fulfilling the requirement that completed tasks must not change owners.

Microsoft Learn: Configure table relationship cascading behavior. Section: "Cascade behaviors". Identifies "Cascade Active" as the setting to reassign only records with an active state. Microsoft Docs: Table relationships

Microsoft Power Platform Fundamentals (PL-900): Chapter 3: "Introduction to Microsoft Dataverse". Explains the distinction between Parental, Referential, and Configurable Cascading behaviors.

Microsoft Dataverse SDK Documentation: Entity Relationship Metadata. Details the CascadeType enumeration where Active is defined as cascading the action to all related records in an active state.

Microsoft Learn: Create and edit 1:N (one-to-many) or N:1 (many-to-one) table relationships. Section: "Relationship behavior". Microsoft Docs: 1:N relationships