TMS VCL UI Pack - Install Failed

Since adding 64bit platform to Delphi 10.3.3 via Manage Platforms, I have not been able to install several component packs (VCL and FNC). When installing one component pack, the installer would detect a previous installation, offer to uninstall, but then uninstall a different component pack.
Now I cannot even install VCL UI Pack at all. I am getting Install Failed. The log has multiple errors the last of which is


C:\Users\Public\Documents\Embarcadero\Studio\20.0\Bpl\TMSVCLUIPackPkgWizDXE12.dproj" (Build target) (1) ->
(_PasCoreCompile target) -> 
  TMSVCLUIPackPkgWizDXE12.dpk(31): error E2202: Required package 'rtl' not found [C:\Users\Public\Documents\Embarcadero\Studio\20.0\Bpl\TMSVCLUIPackPkgWizDXE12.dproj]

    0 Warning(s)
    1 Error(s)

Any help appreciated

This sounds like a library path config issue in your IDE.
Please locate the file rtl.dcp on your system and make sure that the folder where this file is located is added to your library path. Then retry to install.