From a clean build/install:

cmake -S . -B build -DCMAKE_INSTALL_PREFIX=install
cmake --build build --config Release --target install

The generated cmake files:

C:/sandbox/work/oss/rapidjson/install/cmake/RapidJSON-targets.cmake
C:/sandbox/work/oss/rapidjson/install/cmake/RapidJSONConfig.cmake
C:/sandbox/work/oss/rapidjson/install/cmake/RapidJSONConfigVersion.cmake

All contain hardcoded paths based on the original build location. This means that I don't think I can easily share the builds to others.

################################################################################
# RapidJSON source dir
set( RapidJSON_SOURCE_DIR "C:/sandbox/work/oss/rapidjson")

################################################################################
# RapidJSON build dir
set( RapidJSON_DIR "C:/sandbox/work/oss/rapidjson/build")

Perhaps I'm doing something wrong?