To install:

Download and unzip the plugin file to your desktop. If the unzipping creates a folder open it to locate the ZSculptyTools_2021.ZSC file and ZSculptyToolsData folder.
Copy the ZSculptyTools_2021.ZSC file and ZSculptyToolsData folder to the ZBrush 2021\ZStartup\ZPlugs64 folder.
Restart ZBrush. The ZSculpty Tools menu is in the Zplugin palette.