Where do you enable a customer-specific field to be available for Uls and reports relevant...

You enable a customer-specific field to be available for UIs and reports relevant for the same business context in the Custom Fields app. The Custom Fields app allows you to create and manage custom fields for business objects in SAP S/4HANA Cloud, public edition. You can define the properties of the custom fields, such as the label, data type, length, and default value. You can also specify the UIs and reports where you want the custom fields to appear, and the business context that determines the visibility and authorization of the custom fields. The Custom Fields app also enables you to activate the custom fields and generate the corresponding CDS views and OData services for consumption by other applications. References = Using the Key-User In-App Extensibility Tools in SAP S/4HANA Cloud Public Edition, Custom Fields and Logic