Business users created with Maintain employee app F2288A are not picked by Manage Workflow app F2190

Hello,

HR integration is not active in the system, and we create Business users with the app Maintain Employee F2288A.

Roles SAP_BR_MANAGER and SAP_BR_PURCHASING_MANAGER assigned to the user.
As specified in SAP note 3287415 - Users not available in Manage Workflow for Purchase Requisitions. 3279729 - No users available in People picker of Manage workflow application.

When maintaining Workflow for Purchase Requisition with Manage Workflow app F2190, I use Recepient assignment by User, and the user is mssing in the People picker T_F2288A.

If I enter it manually, sustem says that this user ID is not valid.

Employees with HR master data are in the list.
Does that mean that for using Flexible Workflow in Purchasing, integration with HR is a must?