Hi Dave,
This type of error is typically caused by either the design package being moved to a different location and Delphi cannot locate the design package, or that Windows cannot locate the corresponding runtime package on the system PATH.
What is odd is that you state that the package loads in Delphi 11. And the runtime packages for both Delphi 11 and 12 reside in the same directory: C:\Program Files (x86)\Raize\CS5\Deploy\Win32.
Please check in Delphi 11 that the packages are indeed loaded. Select Component > Install Packages menu item and see if the CodeSite packages show up in the list. If they are listed, please select one of them and note the directory listed in the status bar.
Next, I would suggest checking your System PATH to ensure that the Raize\CS5\Deploy\Win32 directory is present.
BTW, the design packages are not really necessary to use CodeSite. They are provided merely for backward compatibility for older versions of CodeSite.
Ray