Are you sure you completely uninstalled? I ask this because the PhotoEn demo is called ..ImageEn\Demos\FullApps\PhotoEn3\ImageEx.dproj and the old PhotoEn projects have been removed, so you may have not completely uninstalled older versions.
Anyway I can run ImageEx here with Delphi 10 Seattle and when resizing there is no exception. I did not change the demos code.
With every release we run a script that recompiles every demo and uploads them to our web site. All the exe files on our site have been built with v6.2.0, so if you are seeing compilation errors it is likely to be an issue in your configuration.
In particular, check that your demo files are in a location that has read/write access.