This is an issue affecting users of Windows 7 and 8.0.
Windows 8.1 and above are not affected.
We are working on a solution for this issue. I don’t have an ETA at this time for when it will be resolved.
In the interim, if you start a support conversation at https://support.pixologic.com we can provide you with instructions for how to roll back to 2021.5.1.
If you already have the installer for 2021.5.1 saved in your downloads, you don’t need to start the support conversation. Simply uninstall ZBrush 2021 and delete its folder . Also delete the C:\Users\Public\Public Documents\ZBrushData2021 folder. Then run your ZBrush 2021.5.1 installer.