I have just updated the Delphi Custom Container Pack sources to support Delphi 10.3 Rio. This time it required more than creating the packages for the new version and adding the latest version of the Delphiversions.inc file. When loading the designtime package an EAssertionFailed exception was raised. It turned out that the category sCategoryDelphiNewFiles no longer exists. I have added two fall back categories: sCategoryDelphiIndividualFiles and sCategoryDelphiNew. One of them will hopefully continue to work.
It now compiles and installs. I have not tested it extensively.