When you launch ZBrush it will temporarily display your name in the title bar. This name goes away when you load any Project (.ZPR) file, being replaced with the name of that file.
Some users don't want their name to display. For example, streamers often prefer to not have that info visible on the screen.
There are two ways to work around this:
Edit the Startup ZScript
Because the name is only displayed until a Project is loaded, simply edit your StartupZScript.txt file to add a command to load any default project you wish. Every time ZBrush launches. If it's a small, simple file then the file will actually load almost as fast as the UI is drawn on the screen and nobody will even have a chance to see your name.
Edit Your User Name
You can also change the name that ZBrush displays, replacing it with whatever you want. Please follow these steps:
1) Make sure that your software is closed and then go to your ZBrush (or ZBrushCore) installation folder. (For example, c:\Program Files\Pixologic\ZBrush 2021) There, run the Pixologic License Manager. (With earlier software versions, it's called the Pixologic Deactivation Manager.) At the lower bottom of its window, click the Reset button and confirm when prompted. You can then close that application.
(We have had reports from some users that the Windows update causing this error prevents them from running the Pixologic Deactivation Manager due to a "Side-by-Side Configuration" error. If that happens to you, please see this article for how to fix that: https://pixologic.kayako.com/article/82-this-application-has-failed-to-start-because-the-side-by-side-configuration-is-incorrect-reinstalling-the-application-may-fix-this-problem)
2) Go to My Licenses (https://pixologic.com/my-licenses/login.php) and deactivate this copy of ZBrush.
3) Go to https://login.pixologic.com and edit your User Profile. You need to change your name to whatever you want ZBrush to show. Save the change.
4) Now launch your software. It will ask for activation again. Log in with your Pixologic ID. Don't worry about if the system shows that no activations are currently available; simply select the same serial number that you had previously registered with. When you return to ZBrush (or ZBrushCore) and complete the activation it will pull the edited name from your Profile page. Everything should be fine from there.