Spawned from discussion in https://discourse.cmake.org/t/installation-qt6-qml-application-cross-plattform/7110/8

Consider a target created in a subdirectory and a call to qt_generate_deploy_app_script in the top-level CMakeLists.txt. The installation will fail to deploy plugins.

Reason: qt_generate_deploy_app_script marks the target as to be deployed, and the target finalizer only generates plugin information for this target if the target is marked.
In the outlined setup, the finalizer is run before qt_generate_deploy_app_script.