The project consists of one main SUBDIRS project file, calling this "MyApp.pro", an "App.pro" with TEMPLATE=app and two subprojects, each of which have TEMPLATE=lib. These "lib" subprojects are responsible for generating one static library each. The source code is organized like this -- the folders marked with "SCM" are under source code management, and any build folders or binary files, should be placed outside of these:

  MyApp
  ├── 3rd_party  <== SCM 'REPO_THIRD'
  │   ├── lib_1
  │   │   └── src
  │   └── lib_2
  │       └── src
  └── App  <== SCM 'REPO_APP'
      ├── include
      ├── qrc
      ├── src
      ├── translations
      └── ui
      App.pro
      MyApp.pro 
      Lib_1.pro
      Lib_2.pro

I know that it is unusual to have all of the .pro files in the same folder as the main project, but this works out well. I can get MyApp.pro to build the application correctly with this as my default build in "Preferences":

../build/%{Project:Name}/%{Qt:Version}/%{BuildConfig:Name}

This results in the following shadowed build folder after opening the main "MyApp" project file in Qt Creator when I click on "Projects" in the task bar:

MyApp/build/MyApp/6.10.2/Debug

using a kit for Qt 6.10.2, for example, building in Debug mode. I create a "lib" folder parallel to the "build" folder in the library projects by setting DESTDIR and TARGET appropriately.

Since I would eventually like to migrate the qmake build to CMake (or at least offer a CMake build as an alternative to the qmake build), the folder structure should end up looking something like this:

  MyApp
  ├── build
  │   ├── appbuild 
  │   │   ├── Debug
  │   │   └── Release
  │   └── libbuild
  │       ├── Debug
  │       └── Release
  ├── 3rd_party  <== SCM 'REPO_THIRD'
  │   ├── Lib_1
  │   │   └── src
  │   └── Lib_2
  │       └── src
  └── App  <== SCM 'REPO_APP'
(etc.)

That way, the "build" subfolder can be created in the traditional (?) CMake fashion either in Creator or by doing cmake -B build from the project directory.

But what is the trick for getting the strings "appbuild" and "libbuild" into the "Default Build Directory" setting? I don't want to have to manually edit the shadow build directory for each configuration. Ideally, one should be able to write %{Project:Template} to achieve this, but i couldn't find anything.