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In app Manage Journal Entries, Setting "Journal Entry Created By" shows the User ID and Full Name, in the Header of the details screen, "Created by" shows the User ID only.
SAP S/4HANA Cloud
Reproducing the Issue
Open app Manage Journal Entries, Go into one journal entry, you will see only user number display, but full name is missing.
To add the Full Name in the header of the details screen adapt UI:
KBA 3041720 - How to add fields to journal entry apps - S/4HANA Could
KBA 3000726 - Full Name field is XXXXX in Display Line Items in General Ledger
SAP Help Portal - Adapting SAP Fiori UIs at Runtime - Key User Adaptation
Manage Journal Entries, F0717, Full Name, User Name, Adapt UI, Journal Entry Created By, User ID , KBA , FI-FIO-GL-TRA , Transaction Apps , How To