Terminate Accrual Subobject Prematurely | Closing Posing Account not maintainable

I want to terminate an accrual object.

In transaction ACACTREE02 I want to set the Closing Posing Accounts but those are greyed out.

How can I customize the system that those fields are maintainable and the closing positing is posted correctly?

For reference this is on an S/4HANA System 1909. We migrated the accrual engine from an ERP R/3 System. In the old system those fields where maintainable in the S/4 System not.

The problem occurs for old and new created accrual objects.