It has been observed that special characters are not being saved correctly in the application, when used against the "Username" field. For example, "StÉphanie" gets converted to "StÃ©phanie".
The Clarity User accounts were being created through an automation, that relied on 3rd-party applications to feed data into it. One of these 3rd-party applications was responsible for the incorrect handling of special characters.
No issue observed with using special characters in the "Username" field. A sample screenshot of how it renders in the application is shown below.