Hi @k Jules2 ,
Welcome to our forum!
In order to further confirm if the issue is related to Outlook desktop client, please log in to OWA and check if the new name is displayed.
If the new name is displayed in OWA, it is suggested that you could try to create a new Outlook profile (Control Panel>Mail>Show Profiles>add) and add the account for testing to check if there are some differences.
Hope the above help!
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