This is very much the same bug as https://bugreports.qt.io/browse/QTBUG-27936.

Using CMake with complicated includes like boost with qt_standard_project_setup takes 2.75 hours for our solution.

If I hack out the two pieces of code in Qt6LinguiestToolsMacros.cmake that append include directories from the target, it finishes correctly in 2 seconds.

Here are the changes I needed to make.

          # get_directory_property(_inc_DIRS INCLUDE_DIRECTORIES)
          # foreach(_pro_include ${_inc_DIRS})
          #     get_filename_component(_abs_include "${_pro_include}" ABSOLUTE)
          #     set(_lst_file_srcs "-I${_pro_include}\n${_lst_file_srcs}")
          # endforeach()

        # set(includePaths "$<TARGET_PROPERTY:${target},INCLUDE_DIRECTORIES>")

Update:

It turns out, I only need to comment out the single line to have it finish in a couple seconds:

        # set(includePaths "$<TARGET_PROPERTY:${target},INCLUDE_DIRECTORIES>")