I have an app, an interface library and plugins.
I define the targets in the main lists file.
Plugins are included using add_subdirectory(plugins).
I want plugins to be able to use find_package in the build and install tree.
I exported targets like this

include(CMakePackageConfigHelpers)

set(LIB_EXPORT_NAME AlbertTargets)
set(LIB_TARGETS_FILE "${LIB_EXPORT_NAME}.cmake")
set(LIB_CONFIG_FILE "AlbertConfig.cmake")
set(LIB_VERSION_FILE "AlbertConfigVersion.cmake")
set(LIB_MACROS_FILE "AlbertMacros.cmake")
set(LIB_CMAKE_MODULE_DIR "${PROJECT_SOURCE_DIR}/cmake")
set(INSTALL_CONFIGDIR "${CMAKE_INSTALL_LIBDIR}/cmake/Albert")

# Install the target
# https://cmake.org/cmake/help/latest/command/install.html#targets
install(
    TARGETS ${TARGET_LIB}
    EXPORT ${LIB_EXPORT_NAME}  # just an association
    FRAMEWORK DESTINATION .
    INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/albert
)

include(CMakePackageConfigHelpers)

# Create version file in build tree
write_basic_package_version_file(
    "${PROJECT_BINARY_DIR}/${LIB_VERSION_FILE}"
    VERSION "${PROJECT_VERSION}"
    COMPATIBILITY AnyNewerVersion
)

# Create config file in build tree
configure_package_config_file(
   "${LIB_CMAKE_MODULE_DIR}/${LIB_CONFIG_FILE}.in"
   "${PROJECT_BINARY_DIR}/${LIB_CONFIG_FILE}"
   INSTALL_DESTINATION ${INSTALL_CONFIGDIR}
)

# Copy the macros to the build directory
configure_file(
    "${LIB_CMAKE_MODULE_DIR}/${LIB_MACROS_FILE}"
    "${PROJECT_BINARY_DIR}/${LIB_MACROS_FILE}"
    COPYONLY
)

# Create a targets file in install tree
# https://cmake.org/cmake/help/latest/command/install.html#export
# By default the generated file will be called <export-name>.cmake
install(
    EXPORT ${LIB_EXPORT_NAME}
    # NAMESPACE ${PROJECT_NAME}::
    DESTINATION ${INSTALL_CONFIGDIR}
)

# Create a targets file in build tree (matching install(EXPORT))
# https://cmake.org/cmake/help/latest/command/export.html#exporting-targets-matching-install-export
# Seems like a shorthand for export(TARGETS)
export(
   EXPORT ${LIB_EXPORT_NAME}
   # NAMESPACE ${PROJECT_NAME}::
   FILE "${CMAKE_BINARY_DIR}/${LIB_TARGETS_FILE}"
)

install(FILES
    "${PROJECT_BINARY_DIR}/${LIB_CONFIG_FILE}"
    "${PROJECT_BINARY_DIR}/${LIB_VERSION_FILE}"
    "${PROJECT_BINARY_DIR}/${LIB_MACROS_FILE}"
    DESTINATION ${INSTALL_CONFIGDIR}
)

# Add bin dir to the prefix path such that plugins in the source tree
# can find albert using find_package
list(APPEND CMAKE_PREFIX_PATH "${CMAKE_BINARY_DIR}")
message(STATUS "CMAKE_PREFIX_PATH: ${CMAKE_PREFIX_PATH}")

However when building the project in the build tree cmake complains about the missing targets file.
If I comment the add_subdirectory(plugins) line the targets file is created.
Is add subdir preferred over export(EXPORT?
What can I do to export the targets before the plugins are processed?
Or in general how can I achieve that the plugins are able to call find_package(…) to find the interface library in the build tree or on the system?